text: On April 25, 2019, Shannon Ryan, who was previously Fox Television chief marketing officer, was made president of marketing for ABC Entertainment and Disney Television Studios, she will report directly to Karey Burke, president of ABC Entertainment, and Craig Hunegs, president of Disney Television Studios.


title: Acquisition of 21st Century Fox by Disney

text: Sinclair Broadcast Group agreed on April 26, 2019 to acquire Fox Sports Networks (excluding YES Network, being sold separately to Yankee Global Enterprises) from Disney for $10 billion. On May 14, 2019, Disney announced it had assumed control of Hulu as part of a put/call agreement with Comcast and its 33% stake in the service. Comcast will continue to license NBCUniversal content and live carriage of NBCUniversal channels until late 2024 and their stake in Hulu could be sold to Disney as early as January of that year. In addition, both companies will fund Hulu's purchase of AT&T's 9.5% stake in Hulu.


text: Following the acquisition, Disney reorganized its television division to align various operations. On June 10, 2019, Disney announced that both Disney Television Studios and FX Entertainment would share the same casting division. On July 31, 2019, Disney reorganized Hulu's reporting structure, placing Hulu's Scripted Originals team under Walt Disney Television. Under the new structure, Hulu's SVP of Original Scripted Content would report directly to the chairman of Disney Television Studios and ABC Entertainment.


text: Fox Stage Productions on July 3, 2019 was moved into Disney Theatrical Group as Buena Vista Theatrical division with all top executives leaving at that time. On August 1, 2019, Disney announced that the Fox Research Library will be folded into the Walt Disney Archives and Disney Imagineering Archives by January 2020.


text: On August 7, 2019, Disney announced that they would overhaul Fox film projects in development except "Avatar", "Planet of the Apes" and "Kingsman" sequels due to "Dark Phoenix" causing a third-quarter loss. A new reduced slate of about 10 films per year fully overseen by Disney will now be the main focus, with 20th Century Fox making half of the films for Hulu and Disney+. Fox properties such as "Home Alone", "Night at the Museum", "Cheaper by the Dozen", and "Diary of a Wimpy Kid" have been assigned for Disney+ release and assigned to Fox Family.


text: On August 9, 2019, the "Los Angeles Times" reported that Disney would be pulling all Fox film library titles out of all theater chains and moving them onto either Hulu or Disney+. Little Theatre, a local theater chain in Rochester, New York, was forced to cancel their August 5 screening of "Fight Club" after Disney notified the theater that it was not allowed to screen the film in the future.


text: On August 22, 2019, Sinclair completed its acquisition of Fox Sports Networks from Disney. Seven days later, the Yankees/Sinclair/Amazon consortium also completed the acquisition of the 80% share of YES Network from Disney on August 29, 2019 with the Yankees owning 65%, Sinclair owning 20% and Amazon owning the remaining 15%.


text: On September 10, 2019, Disney announced their plans to sell the video game division of FoxNext, preferring to license its properties for video games rather than develop them.


text: On October 22, 2019, the Banijay Group announced its intent to acquire Endemol Shine Group from Disney and Apollo Global Management for $2.2 billion. Disney and Apollo agreed to sell Endemol to Banijay on October 26, 2019, pending antitrust approval from regulators. On July 3, 2020, Banijay completed its purchase of Endemol Shine.


text: On October 24, "Vulture" reported that Disney was limiting theatrical exhibitions of Fox's older films, with several theaters and film programmers reporting that Fox's back catalogue was no longer available to them.


text: In January 2020, Disney began to rebrand Fox's studios to remove references to "Fox" from their names, with 20th Century Fox being renamed "20th Century Studios", and Fox Searchlight Pictures being renamed "Searchlight Pictures".


text: On January 22, 2020, Disney announced it had sold off a majority of FoxNext's assets, including FoxNext Games Los Angeles, Cold Iron Studios, Aftershock development studios and FoxNext's original IP's, to mobile game developer Scopely. On January 24, 2020, Disney announced they would shutter Fogbank Entertainment.


text: On January 31, 2020, Disney eliminated the role of Hulu CEO, as part of fully integrating Hulu with Disney's business model. Under the new structure, top Hulu executives would report directly to DTCI and Walt Disney Television leads.


text: On March 17, 2020, "The Wall Street Journal" reported that Disney is looking to sell TrueX due to lack of investment after being label a noncore asset.


text: On May 6, 2020, Brazil's antitrust agency CADE approved the merger between Fox Sports Brazil and ESPN Brasil with conditions requiring Disney to keep Fox Sports Brazil until January 1, 2022, when the channel's operations are expected to be absorbed into ESPN. In the meantime, ESPN and Fox Sports will share the rights to broadcasting sporting events.


text: On August 10, 2020, Disney announced a reorganization and rebranding of its television studios, with 20th Century Fox Television being subsumed by 20th Television, and Fox 21 Television Studios being rebranded as Touchstone Television (reviving a name dropped in 2007 by what then became ABC Studios — which itself was renamed ABC Signature).


text: On October 1, 2020, Disney and Eredivisie jointly announced that Fox Sports (Netherlands) channels would be rebranded as ESPN. The rebranding is a direct consequence of the acquisition and it occurred on January 1, 2021. Like 21st Century Fox before it, Disney owns 51% of Eredivisie Media & Marketing CV while Eredivisie owns the remaining 49%. Eredivisie Media & Marketing in turn owns Fox (Netherlands) and Fox Sports (Netherlands).


text: On November 27, 2020, Disney announced that they would be renaming the Fox branded channels in Latin America to Star on February 22, 2021: Fox Channel becomes Star Channel, Fox Life becomes Star Life etc. No rebrand for the Indian feeds has been announced as of July 26, 2021.


text: On December 30, 2020, Dutch cable provider Ziggo revealed that the European feeds of StarPlus and Star Gold will be rebranded as Utsav Plus and Utsav Gold respectively. The rebranding comes as Disney will use the Star brand name for non-family and mature-oriented programming with its forthcoming hub on Disney+ in several international markets as well as the launch of streaming service Star+ in Latin America.


text: On February 9, 2021, "Deadline Hollywood" confirmed that Blue Sky Studios would shut down due to "current economic realities" related to the COVID-19 pandemic and that all of the Blue Sky Studios library and IPs are absorbed by Disney. Blue Sky Studios was shut down on April 10, 2021.


text: Fox Sports Networks and Fox College Sports were later rebranded as Bally Sports and Stadium College Sports on March 31, 2021.


text: In March 2021, Disney launched a new 20th Television Animation division for adult animation productions from studios involved in this acquisition.


text: On April 27, 2021, Disney announced that most of Fox Networks Group Asia Pacific linear channels will be shut down in two phases in October 2021 for Hong Kong and Southeast Asian countries and January 2022 for Taiwan, respectively. Disney retaining National Geographic, Nat Geo Wild, Star Chinese Channel, and Star Chinese Movies in that region.


text: On May 14, 2021, Fox 2000 Pictures was shut down by Disney after "The Woman in the Window" was released on Netflix.


text: Disney sold Fox Sports Mexico to Grupo Multimedia Lauman in June 2021. Disney was required to sell Fox Sports Mexico as part of the conditions of approval to the 21st Century Fox acquisition in Mexico. Mexican regulators have approved the sale of Fox Sports Mexico to Grupo Multimedia Lauman from Disney. It meets the regulatory requirements of the acquisition process in Mexico.


text: On August 31, 2021, Disney announced that Hotstar in the United States will be shut down in late 2022. The company also announced that they will be migrating content like Hotstar Specials, Star India's programming, and blockbuster movies to Hulu starting September 1, 2021. The sports content including the Indian Premier League, Board of Control for Cricket in India, International Cricket Council, and Pro Kabaddi League will be migrated to ESPN+. Disney wants Hotstar users to sign up for their Disney streaming bundle of Disney+, Hulu, and ESPN+ in the U.S.. Disney acquired Hotstar through its acquisition of 21st Century Fox.


text: On October 28, 2021, ViacomCBS (now Paramount Global) announced that it is acquiring TeleColombia from Disney with the acquisition expecting approval in 2022. TeleColombia was sold on November 23, 2021.


text: On November 4, 2021, Disney announced that they would rebrand the remaining feeds of Fox Sports Latin America to ESPN 4 on December 1, 2021 with the exception of Mexico due to Disney selling Fox Sports Mexico to Grupo Multimedia Lauman.


text: On January 20, 2022, CNDC ordered Disney to sell the Fox Sports Argentina television network from the 21st Century Fox purchase in order to get an approval from the government of Argentina. On February 15, 2022, Disney announced it sold Fox Sports Argentina to Mediapro. The sale would be approved by the CNDC on April 27, 2022.<ref name="Mediapro/Argentina"></ref>


text: On March 1, 2022, TrueX was rebranded into Infillion by Gimbal, approximately one year after it was sold to Gimbal by Disney.


text: It was announced that on May 1, 2022, Fox Sports Premium would rebrand to ESPN Premium following Disney acquisition of 21st Century Fox to reflect on that change.


text: Despite Disney passing antitrust approval from regulators in every country, critics of Disney's purchase expressed significant antitrust concerns. The deal is a horizontal merger (i.e., in which a company buys up a corporation that produces the same goods and products) as opposed to a vertical merger (i.e., two companies that operate at separate stages of the production process for a specific finished product), much akin to the integrations of AT&T–Time Warner and Comcast–NBC Universal. Horizontal mergers are more likely to be disapproved than vertical mergers, as they affect a more tangible reduction in competition. The Federal Trade Commission (FTC) states on its website that "The greatest antitrust concern arises with proposed mergers between direct competitors (horizontal mergers)."


text: As both Disney and Fox produce films and television series, the deal reduced the number of major film studios in Hollywood from six to five. Some argued the operation would still leave many competitors around since Disney may compete with Netflix in the online streaming market with Disney+ and Hulu in equal conditions with its newly acquired properties. Opponents countered that these arguments do not hold much weight due to Disney's powerful box office and stock market shares, its practices, and its purchase of Fox's many assets.


text: A film reporter said, "They'll have more control over more things, so if they decide they don't like what you wrote and want to ban you from their screenings, eventually that will mean all of entertainment. For journalists and reporters trying to do their job, it is frightening to see the scope of one company expand in that way and know that your fate is kind of tied up with them." "We've seen a pattern in Disney's behavior. The more power they have, the more they wield it," one entertainment reporter said. A freelance critic and member of the New York Film Critics Circle said that they were troubled by the idea of the Disney–Fox deal.


text: On November 3, 2017, Disney banned the "Los Angeles Times" from attending press screenings of its films in retaliation for the paper's coverage of their political influence in Anaheim, California in September of that year. On November 7, however, Disney reversed its decision, after receiving massive protests and condemnation from a number of major publications and writers including "The New York Times", "The Boston Globe" critic Ty Burr, "The Washington Post" blogger Alyssa Rosenberg, "A Wrinkle in Time" director Ava DuVernay, the websites "The A.V. Club" and "Flavorwire", and film critic organizations which threatened to disqualify Disney films from their year-end awards in retaliation, specifically, the National Society of Film Critics, Los Angeles Film Critics Association, New York Film Critics Circle, and Boston Society of Film Critics.


text: Jason Bailey, the editor of "Flavorwire", thought the way Disney treated the "Los Angeles Times" was "absolutely chilling", fearing it would only grow more common after the merger:


text: One film writer stated that "I personally worry that a studio this big will need the press less and less. I don't think anything drastic will change immediately, but I think it is more important than ever for entertainment reporters to uphold journalistic values. We are not their PR arms, no matter how much they'd like us to be." Another film reporter said, "As a critic, I've had Disney tell me they don't want to invite me to [its] film because I didn't like the last one. It really scares me to watch them get even more power."


text: Unlike other studios, Disney has a reputation for strict conditions being forced upon theater owners for its films, such as "" and "". For the latter, Disney demanded a 65% cut of domestic ticket sales (rather than the minimum 55% to 60% cut) along with a four-week hold in each venue, and a 5% penalty to any theater owner who breaks any part of the contract, including taking the film off-screen. If the Disney–Fox deal had happened in late 2016, Disney's domestic box office in 2017 would have equaled $4.5 billion or 40% market share, a figure no major studio has ever hit. For some, the deal would give Disney unprecedented market power in the industry.


text: One distribution studio executive denounced the deal, saying that "If I was an independent mom-and-pop theater, I would just close down; there's no way to survive. With a 40% market share, how do you negotiate against that?" John Roper, the general manager of the Phoenix Theatre in Fort Nelson, British Columbia, said that Disney/Fox had him worried about even stricter rules in the future, stating, "It's not good for any type of industry when a company grows that large. Disney holds all the cards, and we have to play by their rules. Smaller cinemas are just left in the dust." Roper decided not to screen "Star Wars: The Last Jedi" because of Disney's strict conditions of requiring the theater to run the film four weeks straight and play it four times a day (as opposed to other studios, who only require a minimum of two weeks for a film run and play it one time a day). Elkader Cinema in Elkader, Iowa, opted out the movie for the same reason, with owner Lee Akin stating that "I can't get the entire town in my auditorium in one week's time let alone four."


text: In Brazil, Disney demanded a 52% cut of "Coco"s domestic ticket sales (rather than the historical 50% cut) and some theaters (with exceptions including foreign chains, such as Cinemark Theatres and Cinépolis) boycotted the film. "Coco" was shown in 618 screens, against 919 screens that showed Sony Pictures' "".


text: On November 22, 2019, the U.S. Department of Justice formally filed its motion for a federal court order to nullify the Paramount Decrees, which was set in place after the 1948 case "United States v. Paramount Pictures, Inc." that required movie studios to divest themselves of their theatrical arms, and prohibited certain anti-competitive practices in the distribution business. The Department had cited the shifting realities of an industry that has come to rely on online revenue such as streaming services as a justification. David Sims of "The Atlantic" wrote that such move would be very disruptive to the theater industry:


text: The National Association of Theatre Owners (NATO), which represents major theater chains, expressed its concern about the murky future the DOJ could create, saying "If exhibitors were forced to book out the vast majority of their screens on major studio films for most of the year, this would leave little to no room for important films from smaller studios."


text: American Cable Association President and CEO Matthew M. Polka lambasted the deal and called on federal regulators to "fully investigate" the merger. He was concerned about his smaller subscription television constituents having to negotiate multichannel deals with a behemoth that combines Fox's regional sports networks with ESPN and its cadre of collegiate-conference-focused RSNs, as well as the majority stake in Hulu:


text: Many European telecommunication companies also expressed concerns about the Disney–Fox deal, considering that Sky plc and Sky UK were included in the package, as it serves almost 23 million households across Britain, Ireland, Germany, Austria, and Italy. Disney's takeover of Sky would be greater than RTL Group, Mediaset, ITV, ProSiebenSat.1 Media, Viasat, and Vivendi combined, according to Eikon estimates, and could allow Sky to expand into new markets and bid more for sports rights and other content. Some felt that a Disney-owned Sky UK would be most damaging to its pay-TV competitors since it has invested in content to cross-sell television with mobile services, in a bid to squeeze more out of customers. A hedge fund with a small stake in Sky has complained that the Disney–Fox deal could cost minority shareholders in the UK satellite broadcaster a hefty premium unless UK regulators intervene.


text: Dish Network CEO Erik Carlson said blockbuster mergers like the Disney–Fox deal could severely limit the number of content companies providing to their customers. Carlson said on CNBC's "Squawk on the Street" that "We really take the position that we think about the customer and the customer first."


text: The Writers Guild of America West, the union that represents writers of films, television, and other media, wrote that:


text: Tom Rothman, chairman of the Sony Pictures Entertainment Motion Picture Group and former co-chairman of Fox Filmed Entertainment, said the Disney–Fox deal was a dangerous proposition: "Consolidation under giant corporate mandates rarely promotes creative risk-taking. And in the long run, it is always a challenge to compete against horizontal monopolistic power."


text: James Mangold, director of Fox's Marvel adaptations "The Wolverine" and its R-rated sequel "Logan", expressed concerns that the deal might lead to the approval of a similar film that may have more limited appeal than a conventional Marvel blockbuster, thereby limiting the opportunities for certain filmmakers as well as the consumers. Mangold said that "If they're actually changing their mandate, if what they're supposed to do alters, that would be sad to me because it just means less movies."


text: At the Critics' Choice Movie Awards on January 11, 2018, producer J. Miles Dale, who accepted the Critics' Choice Movie Award for Best Picture for "The Shape of Water", urged Disney "not to mess" with 20th Century Fox's indie studio Fox Searchlight Pictures, saying, "they're making the kind of movies that we need to make, we want to make, and people need to see."


text: Writer Marc Guggenheim, known for his work for the Arrowverse for The CW, said that "As a writer, I'm not a big fan of these big corporate consolidations. I don't think they're necessarily good for writers, directors, producers, and actors. I also, as an American, don't love these big corporate mergers. I don't think they're necessarily good for the country."


text: The potential acquisition of Fox by Disney caused concern within the entertainment industry that smaller media companies, including Viacom, CBS Corporation, Lionsgate, and Metro-Goldwyn-Mayer, would need to consolidate or be sold in order to remain competitive.


text: On February 13, 2018, television producer Ryan Murphy, a long-time collaborator of 20th Century Fox Television, signed a five-year $300 million agreement with Netflix, a move considered to be a big blow to Fox and Disney. Murphy cited the Disney–Fox deal as the main reason for departure, arguing that his freedom under Disney might be severely limited in creating new, risk-taking content.


text: Jeff Bock of Exhibitor Relations expressed hope that the merger would force creativity in other studios like Paramount, which might focus on smaller-budget films knowing that it could not compete with Walt Disney (after the Fox acquisition) in making big-budget blockbusters.


text: Viacom CEO Bob Bakish has stated that the Disney–Fox deal provides a "very real opportunity" to hire new executive and creative talent at Paramount and other studios amid the "dislocation associated with change of ownership" at Disney and Fox. Bakish also suggested that Viacom and other companies can provide new content for streaming services such as Netflix once Disney removes their content from the service in 2019.


text: Walt Disney Studios co-chairman and CEO Alan F. Horn acknowledged that Disney has a stranglehold on the entertainment industry especially after the Fox acquisition, but defended against the monopoly accusations:


text: Tom Reimann of "Collider" said that "Horn's bizarre, rambling rationalization veers towards seemingly deliberate obfuscation at several points" by saying that he "point[ed] out that Disney makes a wide variety of films (the two topics are wholly unrelated) while admitting only that Disney enjoys 'a very hefty percentage of the box office' without acknowledging that the studio has bought out most of its meaningful competition."


text: Former President Donald Trump praised both companies for the merger, believing it is best for American jobs. However, U.S. Representative David Cicilline of Rhode Island, the ranking Democrat on the House Antitrust Subcommittee, expressed concerns over the transaction. He said in a statement that "Disney's proposed purchase of 21st Century Fox threatens to put control of even more television, movie, and news content into the hands of a single media giant. If it's approved, this acquisition could allow Disney to limit what consumers can watch and increase their cable bills," he said. "Disney will gain more than 300 channels, 22 regional sports networks, control over Hulu, and a significant portion of Roku."


text: Richard Greenfield, a BTIG Research analyst, wrote that the combined Disney and Fox assets would have a 39% theatrical market share:


text: In response to the Disney–Fox deal, analyst Andy Hargreaves of KeyBanc Capital Markets Inc. downgraded Fox's stock from overweight to Sector Weight with no assigned price target. Hargreaves said that although the merger is positive for both companies, it comes with a high antitrust risk due to Disney's potential share of theatrical revenue, its share of domestic cable assets, its strong position in sports, and its power to already force preferential deals with cable, satellite, and theater owners.


text: David Balto, an antitrust lawyer and former policy director at the FTC, said that the inclusion of regional sports networks would give Disney greater leverage with cable and satellite distributors: "Any increase in Disney sports programming will be extremely problematic and will get intense scrutiny".


text: John Simpson of the activist group Consumer Watchdog said that the deal "would give far too much monopolistic power to Disney, which is known for cutthroat, hardball tactics", and "can only mean higher prices and less choice for consumers."


text: Barton Crockett, a media analyst at B. Riley FBR, said that "Disney is becoming the Wal-Mart of Hollywood: huge and dominant. That's going to have a big influence up and down the supply chain."


text: Ian Bezek, contributor to "InvestorPlace", questioned the underlying rationale for the merger, asking why Disney needed to acquire Fox's film production and cable sports business for such a "high price", given Disney's already healthy positions in both businesses:


text: Jonathan Barnett, law professor at the University of Southern California Gould School of Law states that when considering streaming services under the same markets as theaters, worries about Disney's control "would be substantially diminished".


text: On November 14, 2018, it was revealed that a new independent company, which was tentatively called "New Fox", would be named Fox Corporation. The company implemented its structure on January 1, 2019. Its assets include Fox's broadcast, news and sports businesses. They include:


text: Assets that were initially included in the acquisition, but have since been sold off to third parties.


title: Ordinary least squares

text: In statistics, ordinary least squares (OLS) is a type of linear least squares method for choosing the unknown parameters in a linear regression model (with fixed level-one effects of a linear function of a set of explanatory variables) by the principle of least squares: minimizing the sum of the squares of the differences between the observed dependent variable (values of the variable being observed) in the input dataset and the output of the (linear) function of the independent variable.


title: Ordinary least squares

text: Geometrically, this is seen as the sum of the squared distances, parallel to the axis of the dependent variable, between each data point in the set and the corresponding point on the regression surface—the smaller the differences, the better the model fits the data. The resulting estimator can be expressed by a simple formula, especially in the case of a simple linear regression, in which there is a single regressor on the right side of the regression equation.


title: Ordinary least squares

text: The OLS estimator is consistent for the level-one fixed effects when the regressors are exogenous and forms perfect colinearity (rank condition), consistent for the variance estimate of the residuals when regressors have finite fourth moments and—by the Gauss–Markov theorem—optimal in the class of linear unbiased estimators when the errors are homoscedastic and serially uncorrelated. Under these conditions, the method of OLS provides minimum-variance mean-unbiased estimation when the errors have finite variances. Under the additional assumption that the errors are normally distributed with zero mean, OLS is the maximum likelihood estimator that outperforms any non-linear unbiased estimator.


title: Ordinary least squares

text: Suppose the data consists of formula_1 observations formula_2. Each observation formula_3 includes a scalar response formula_4 and a column vector formula_5 of formula_6 parameters (regressors), i.e., formula_7. In a linear regression model, the response variable, formula_4, is a linear function of the regressors:


title: Ordinary least squares

text: where formula_5, as introduced previously, is a column vector of the formula_3-th observation of all the explanatory variables; formula_13 is a formula_14 vector of unknown parameters; and the scalar formula_15 represents unobserved random variables (errors) of the formula_3-th observation. formula_15 accounts for the influences upon the responses formula_4 from sources other than the explanators formula_5. This model can also be written in matrix notation as


title: Ordinary least squares

text: where formula_21 and formula_22 are formula_23 vectors of the response variables and the errors of the formula_24 observations, and formula_25 is an formula_26 matrix of regressors, also sometimes called the design matrix, whose row formula_3 is formula_28 and contains the formula_3-th observations on all the explanatory variables.


title: Ordinary least squares

text: As a rule, the constant term is always included in the set of regressors formula_25, say, by taking formula_31 for all formula_32. The coefficient formula_33 corresponding to this regressor is called the "intercept".


title: Ordinary least squares

text: Regressors do not have to be independent: there can be any desired relationship between the regressors (so long as it is not a linear relationship). For instance, we might suspect the response depends linearly both on a value and its square; in which case we would include one regressor whose value is just the square of another regressor. In that case, the model would be "quadratic" in the second regressor, but none-the-less is still considered a "linear" model because the model "is" still linear in the parameters (formula_13).


title: Ordinary least squares

text: of formula_24 linear equations in formula_6 unknown coefficients, formula_38, with formula_39. (Note: for a linear model as above, not all elements in formula_40 contains information on the data points. The first column is populated with ones, formula_41. Only the other columns contain actual data. So here formula_6 is equal to the number of regressors plus one.) This can be written in matrix form as


title: Ordinary least squares

text: Such a system usually has no exact solution, so the goal is instead to find the coefficients formula_13 which fit the equations "best", in the sense of solving the quadratic minimization problem


title: Ordinary least squares

text: A justification for choosing this criterion is given in Properties below. This minimization problem has a unique solution, provided that the formula_6 columns of the matrix formula_40 are linearly independent, given by solving the so-called "normal equations":


title: Ordinary least squares

text: Suppose "b" is a "candidate" value for the parameter vector "β". The quantity , called the residual for the "i"-th observation, measures the vertical distance between the data point and the hyperplane , and thus assesses the degree of fit between the actual data and the model. The sum of squared residuals (SSR) (also called the error sum of squares (ESS) or residual sum of squares (RSS)) is a measure of the overall model fit:


title: Ordinary least squares

text: where "T" denotes the matrix transpose, and the rows of "X", denoting the values of all the independent variables associated with a particular value of the dependent variable, are "X = x". The value of "b" which minimizes this sum is called the OLS estimator for "β". The function "S"("b") is quadratic in "b" with positive-definite Hessian, and therefore this function possesses a unique global minimum at formula_58, which can be given by the explicit formula:


title: Ordinary least squares

text: The product "N"="X" "X" is a Gram matrix and its inverse, "Q"="N", is the "cofactor matrix" of "β", closely related to its covariance matrix, "C".


title: Ordinary least squares

text: The matrix ("X" "X") "X"="Q" "X" is called the Moore–Penrose pseudoinverse matrix of X. This formulation highlights the point that estimation can be carried out if, and only if, there is no perfect multicollinearity between the explanatory variables (which would cause the gram matrix to have no inverse).


title: Ordinary least squares

text: where "P" = "X"("X""X")"X" is the projection matrix onto the space "V" spanned by the columns of "X". This matrix "P" is also sometimes called the hat matrix because it "puts a hat" onto the variable "y". Another matrix, closely related to "P" is the "annihilator" matrix ; this is a projection matrix onto the space orthogonal to "V". Both matrices "P" and "M" are symmetric and idempotent (meaning that and ), and relate to the data matrix "X" via identities and . Matrix "M" creates the residuals from the regression:


title: Ordinary least squares

text: The denominator, "n"−"p", is the statistical degrees of freedom. The first quantity, "s", is the OLS estimate for "σ", whereas the second, formula_63, is the MLE estimate for "σ". The two estimators are quite similar in large samples; the first estimator is always unbiased, while the second estimator is biased but has a smaller mean squared error. In practice "s" is used more often, since it is more convenient for the hypothesis testing. The square root of "s" is called the regression standard error, standard error of the regression, or standard error of the equation.


title: Ordinary least squares

text: It is common to assess the goodness-of-fit of the OLS regression by comparing how much the initial variation in the sample can be reduced by regressing onto "X". The coefficient of determination "R" is defined as a ratio of "explained" variance to the "total" variance of the dependent variable "y", in the cases where the regression sum of squares equals the sum of squares of residuals:


title: Ordinary least squares

text: where TSS is the total sum of squares for the dependent variable, formula_65, and formula_66 is an "n"×"n" matrix of ones. (formula_67 is a centering matrix which is equivalent to regression on a constant; it simply subtracts the mean from a variable.) In order for "R" to be meaningful, the matrix "X" of data on regressors must contain a column vector of ones to represent the constant whose coefficient is the regression intercept. In that case, "R" will always be a number between 0 and 1, with values close to 1 indicating a good degree of fit.


title: Ordinary least squares

text: The variance in the prediction of the independent variable as a function of the dependent variable is given in the article Polynomial least squares.


title: Ordinary least squares

text: If the data matrix "X" contains only two variables, a constant and a scalar regressor "x", then this is called the "simple regression model". This case is often considered in the beginner statistics classes, as it provides much simpler formulas even suitable for manual calculation. The parameters are commonly denoted as :


title: Ordinary least squares

text: Introducing formula_73 and a matrix "K" with the assumption that a matrix formula_74 is non-singular and "K" "X" = 0 (cf. Orthogonal projections), the residual vector should satisfy the following equation:


title: Ordinary least squares

text: Another way of looking at it is to consider the regression line to be a weighted average of the lines passing through the combination of any two points in the dataset. Although this way of calculation is more computationally expensive, it provides a better intuition on OLS.


title: Ordinary least squares

text: The OLS estimator is identical to the maximum likelihood estimator (MLE) under the normality assumption for the error terms. This normality assumption has historical importance, as it provided the basis for the early work in linear regression analysis by Yule and Pearson. From the properties of MLE, we can infer that the OLS estimator is asymptotically efficient (in the sense of attaining the Cramér–Rao bound for variance) if the normality assumption is satisfied.


title: Ordinary least squares

text: In iid case the OLS estimator can also be viewed as a GMM estimator arising from the moment conditions


title: Ordinary least squares

text: These moment conditions state that the regressors should be uncorrelated with the errors. Since "x" is a "p"-vector, the number of moment conditions is equal to the dimension of the parameter vector "β", and thus the system is exactly identified. This is the so-called classical GMM case, when the estimator does not depend on the choice of the weighting matrix.


title: Ordinary least squares

text: Note that the original strict exogeneity assumption implies a far richer set of moment conditions than stated above. In particular, this assumption implies that for any vector-function , the moment condition will hold. However it can be shown using the Gauss–Markov theorem that the optimal choice of function is to take , which results in the moment equation posted above.


title: Ordinary least squares

text: There are several different frameworks in which the linear regression model can be cast in order to make the OLS technique applicable. Each of these settings produces the same formulas and same results. The only difference is the interpretation and the assumptions which have to be imposed in order for the method to give meaningful results. The choice of the applicable framework depends mostly on the nature of data in hand, and on the inference task which has to be performed.


title: Ordinary least squares

text: One of the lines of difference in interpretation is whether to treat the regressors as random variables, or as predefined constants. In the first case (random design) the regressors "x" are random and sampled together with the "y"'s from some population, as in an observational study. This approach allows for more natural study of the asymptotic properties of the estimators. In the other interpretation (fixed design), the regressors "X" are treated as known constants set by a design, and "y" is sampled conditionally on the values of "X" as in an experiment. For practical purposes, this distinction is often unimportant, since estimation and inference is carried out while conditioning on "X". All results stated in this article are within the random design framework.


title: Ordinary least squares

text: The classical model focuses on the "finite sample" estimation and inference, meaning that the number of observations "n" is fixed. This contrasts with the other approaches, which study the asymptotic behavior of OLS, and in which the number of observations is allowed to grow to infinity.


title: Ordinary least squares

text: In some applications, especially with cross-sectional data, an additional assumption is imposed — that all observations are independent and identically distributed. This means that all observations are taken from a random sample which makes all the assumptions listed earlier simpler and easier to interpret. Also this framework allows one to state asymptotic results (as the sample size ), which are understood as a theoretical possibility of fetching new independent observations from the data generating process. The list of assumptions in this case is:


title: Ordinary least squares

text: First of all, under the "strict exogeneity" assumption the OLS estimators formula_83 and "s" are unbiased, meaning that their expected values coincide with the true values of the parameters:


title: Ordinary least squares

text: If the strict exogeneity does not hold (as is the case with many time series models, where exogeneity is assumed only with respect to the past shocks but not the future ones), then these estimators will be biased in finite samples.


title: Ordinary least squares

text: In particular, the standard error of each coefficient formula_87 is equal to square root of the "j"-th diagonal element of this matrix. The estimate of this standard error is obtained by replacing the unknown quantity "σ" with its estimate "s". Thus,


title: Ordinary least squares

text: It can also be easily shown that the estimator formula_83 is uncorrelated with the residuals from the model:


title: Ordinary least squares

text: The "Gauss–Markov theorem" states that under the "spherical errors" assumption (that is, the errors should be uncorrelated and homoscedastic) the estimator formula_83 is efficient in the class of linear unbiased estimators. This is called the "best linear unbiased estimator" (BLUE). Efficiency should be understood as if we were to find some other estimator formula_92 which would be linear in "y" and unbiased, then


title: Ordinary least squares

text: in the sense that this is a nonnegative-definite matrix. This theorem establishes optimality only in the class of linear unbiased estimators, which is quite restrictive. Depending on the distribution of the error terms "ε", other, non-linear estimators may provide better results than OLS.


title: Ordinary least squares

text: The properties listed so far are all valid regardless of the underlying distribution of the error terms. However, if you are willing to assume that the "normality assumption" holds (that is, that ), then additional properties of the OLS estimators can be stated.


title: Ordinary least squares

text: This estimator reaches the Cramér–Rao bound for the model, and thus is optimal in the class of all unbiased estimators. Note that unlike the Gauss–Markov theorem, this result establishes optimality among both linear and non-linear estimators, but only in the case of normally distributed error terms.


title: Ordinary least squares

text: The variance of this estimator is equal to , which does not attain the Cramér–Rao bound of . However it was shown that there are no unbiased estimators of "σ" with variance smaller than that of the estimator "s". If we are willing to allow biased estimators, and consider the class of estimators that are proportional to the sum of squared residuals (SSR) of the model, then the best (in the sense of the mean squared error) estimator in this class will be , which even beats the Cramér–Rao bound in case when there is only one regressor ().


title: Ordinary least squares

text: Moreover, the estimators formula_83 and "s" are independent, the fact which comes in useful when constructing the t- and F-tests for the regression.


title: Ordinary least squares

text: As was mentioned before, the estimator formula_98 is linear in "y", meaning that it represents a linear combination of the dependent variables "y". The weights in this linear combination are functions of the regressors "X", and generally are unequal. The observations with high weights are called influential because they have a more pronounced effect on the value of the estimator.


title: Ordinary least squares

text: To analyze which observations are influential we remove a specific "j"-th observation and consider how much the estimated quantities are going to change (similarly to the jackknife method). It can be shown that the change in the OLS estimator for "β" will be equal to


title: Ordinary least squares

text: where is the "j"-th diagonal element of the hat matrix "P", and "x" is the vector of regressors corresponding to the "j"-th observation. Similarly, the change in the predicted value for "j"-th observation resulting from omitting that observation from the dataset will be equal to


title: Ordinary least squares

text: From the properties of the hat matrix, , and they sum up to "p", so that on average . These quantities "h" are called the leverages, and observations with high "h" are called leverage points. Usually the observations with high leverage ought to be scrutinized more carefully, in case they are erroneous, or outliers, or in some other way atypical of the rest of the dataset.


title: Ordinary least squares

text: Sometimes the variables and corresponding parameters in the regression can be logically split into two groups, so that the regression takes form


title: Ordinary least squares

text: The Frisch–Waugh–Lovell theorem states that in this regression the residuals formula_102 and the OLS estimate formula_103 will be numerically identical to the residuals and the OLS estimate for "β" in the following regression:


title: Ordinary least squares

text: The theorem can be used to establish a number of theoretical results. For example, having a regression with a constant and another regressor is equivalent to subtracting the means from the dependent variable and the regressor and then running the regression for the de-meaned variables but without the constant term.


title: Ordinary least squares

text: where "Q" is a "p"×"q" matrix of full rank, and "c" is a "q"×1 vector of known constants, where . In this case least squares estimation is equivalent to minimizing the sum of squared residuals of the model subject to the constraint "A". The constrained least squares (CLS) estimator can be given by an explicit formula:


title: Ordinary least squares

text: This expression for the constrained estimator is valid as long as the matrix "XX" is invertible. It was assumed from the beginning of this article that this matrix is of full rank, and it was noted that when the rank condition fails, "β" will not be identifiable. However it may happen that adding the restriction "A" makes "β" identifiable, in which case one would like to find the formula for the estimator. The estimator is equal to


title: Ordinary least squares

text: where "R" is a "p"×("p" − "q") matrix such that the matrix is non-singular, and . Such a matrix can always be found, although generally it is not unique. The second formula coincides with the first in case when "XX" is invertible.


title: Ordinary least squares

text: The least squares estimators are point estimates of the linear regression model parameters "β". However, generally we also want to know how close those estimates might be to the true values of parameters. In other words, we want to construct the interval estimates.


title: Ordinary least squares

text: Since we haven't made any assumption about the distribution of error term "ε", it is impossible to infer the distribution of the estimators formula_98 and formula_109. Nevertheless, we can apply the central limit theorem to derive their "asymptotic" properties as sample size "n" goes to infinity. While the sample size is necessarily finite, it is customary to assume that "n" is "large enough" so that the true distribution of the OLS estimator is close to its asymptotic limit.


title: Ordinary least squares

text: We can show that under the model assumptions, the least squares estimator for "β" is consistent (that is formula_98 converges in probability to "β") and asymptotically normal:


title: Ordinary least squares

text: Using this asymptotic distribution, approximate two-sided confidence intervals for the "j"-th component of the vector formula_113 can be constructed as


title: Ordinary least squares

text: where "q" denotes the quantile function of standard normal distribution, and [·] is the "j"-th diagonal element of a matrix.


title: Ordinary least squares

text: Similarly, the least squares estimator for "σ" is also consistent and asymptotically normal (provided that the fourth moment of "ε" exists) with limiting distribution


title: Ordinary least squares

text: These asymptotic distributions can be used for prediction, testing hypotheses, constructing other estimators, etc.. As an example consider the problem of prediction. Suppose formula_116 is some point within the domain of distribution of the regressors, and one wants to know what the response variable would have been at that point. The mean response is the quantity formula_117, whereas the predicted response is formula_118. Clearly the predicted response is a random variable, its distribution can be derived from that of formula_113:


title: Ordinary least squares

text: Two hypothesis tests are particularly widely used. First, one wants to know if the estimated regression equation is any better than simply predicting that all values of the response variable equal its sample mean (if not, it is said to have no explanatory power). The null hypothesis of no explanatory value of the estimated regression is tested using an F-test. If the calculated F-value is found to be large enough to exceed its critical value for the pre-chosen level of significance, the null hypothesis is rejected and the alternative hypothesis, that the regression has explanatory power, is accepted. Otherwise, the null hypothesis of no explanatory power is accepted.


title: Ordinary least squares

text: Second, for each explanatory variable of interest, one wants to know whether its estimated coefficient differs significantly from zero—that is, whether this particular explanatory variable in fact has explanatory power in predicting the response variable. Here the null hypothesis is that the true coefficient is zero. This hypothesis is tested by computing the coefficient's t-statistic, as the ratio of the coefficient estimate to its standard error. If the t-statistic is larger than a predetermined value, the null hypothesis is rejected and the variable is found to have explanatory power, with its coefficient significantly different from zero. Otherwise, the null hypothesis of a zero value of the true coefficient is accepted.


title: Ordinary least squares

text: In addition, the Chow test is used to test whether two subsamples both have the same underlying true coefficient values. The sum of squared residuals of regressions on each of the subsets and on the combined data set are compared by computing an F-statistic; if this exceeds a critical value, the null hypothesis of no difference between the two subsets is rejected; otherwise, it is accepted.


title: Ordinary least squares

text: The following data set gives average heights and weights for American women aged 30–39 (source: "The World Almanac and Book of Facts, 1975").


title: Ordinary least squares

text: When only one dependent variable is being modeled, a scatterplot will suggest the form and strength of the relationship between the dependent variable and regressors. It might also reveal outliers, heteroscedasticity, and other aspects of the data that may complicate the interpretation of a fitted regression model. The scatterplot suggests that the relationship is strong and can be approximated as a quadratic function. OLS can handle non-linear relationships by introducing the regressor . The regression model then becomes a multiple linear model:


title: Ordinary least squares

text: Ordinary least squares analysis often includes the use of diagnostic plots designed to detect departures of the data from the assumed form of the model. These are some of the common diagnostic plots:


title: Ordinary least squares

text: An important consideration when carrying out statistical inference using regression models is how the data were sampled. In this example, the data are averages rather than measurements on individual women. The fit of the model is very good, but this does not imply that the weight of an individual woman can be predicted with high accuracy based only on her height.


title: Ordinary least squares

text: This example also demonstrates that coefficients determined by these calculations are sensitive to how the data is prepared. The heights were originally given rounded to the nearest inch and have been converted and rounded to the nearest centimetre. Since the conversion factor is one inch to 2.54 cm this is "not" an exact conversion. The original inches can be recovered by Round(x/0.0254) and then re-converted to metric without rounding. If this is done the results become:


title: Ordinary least squares

text: Using either of these equations to predict the weight of a 5' 6" (1.6764 m) woman gives similar values: 62.94 kg with rounding vs. 62.98 kg without rounding. Thus a seemingly small variation in the data has a real effect on the coefficients but a small effect on the results of the equation.


title: Ordinary least squares

text: While this may look innocuous in the middle of the data range it could become significant at the extremes or in the case where the fitted model is used to project outside the data range (extrapolation).


title: Ordinary least squares

text: This highlights a common error: this example is an abuse of OLS which inherently requires that the errors in the independent variable (in this case height) are zero or at least negligible. The initial rounding to nearest inch plus any actual measurement errors constitute a finite and non-negligible error. As a result, the fitted parameters are not the best estimates they are presumed to be. Though not totally spurious the error in the estimation will depend upon relative size of the "x" and "y" errors.


title: Ordinary least squares

text: We can use the least square mechanism to figure out the equation of a two body orbit in polar base co-ordinates. The equation typically used is formula_130 where formula_131 is the radius of how far the object is from one of the bodies. In the equation the parameters formula_6 and formula_133 are used to determine the path of the orbit. We have measured the following data.


title: Ordinary least squares

text: First we need to represent e and p in a linear form. So we are going to rewrite the equation formula_131 as formula_137. Now we can use this form to represent our observational data as:


title: Ordinary least squares

text: formula_138 where formula_139 is formula_140 and formula_141 is formula_142 and formula_143 is constructed by the first column being the coefficient of formula_140 and the second column being the coefficient of formula_142 and formula_146 is the values for the respective formula_147 so formula_148 and formula_149


title: Index Librorum Prohibitorum

text: The Index Librorum Prohibitorum ("List of Prohibited Books") was a list of publications deemed heretical or contrary to morality by the Sacred Congregation of the Index (a former Dicastery of the Roman Curia), and Catholics were forbidden to read them.


title: Index Librorum Prohibitorum

text: There were attempts to ban heretical books before the sixteenth century, notably in the ninth-century "Decretum Glasianum"; the "Index of Prohibited Books" of 1560 banned thousands of book titles and blacklisted publications, including the works of Europe's intellectual elites. The 20th and final edition of the index appeared in 1948, and the "Index" was formally abolished on 14 June 1966 by Pope Paul VI.


title: Index Librorum Prohibitorum

text: The "Index" condemned religious and secular texts alike, grading works by the degree to which they were seen to be repugnant to the church. The aim of the list was to protect church members from reading theologically, culturally, or politically disruptive books. Such books included works by astronomers, such as the German Johannes Kepler's "Epitome Astronomiae Copernicanae" (published in three volumes from 1618 to 1621), which was on the Index from 1621 to 1835, works by philosophers, such as the Prussian Immanuel Kant's "Critique of Pure Reason" (1781), and editions and translations of the Bible that had not been approved. Editions of the "Index" also contained the rules of the Church relating to the reading, selling, and preemptive censorship of books.


title: Index Librorum Prohibitorum

text: The canon law of the Latin Church still recommends that works should be submitted to the judgment of the local ordinary if they concern sacred Scripture, theology, canon law, or church history, religion or morals. The local ordinary consults someone whom he considers competent to give a judgment and, if that person gives the "nihil obstat" ("nothing forbids"), the local ordinary grants the "imprimatur" ("let it be printed"). Members of religious institutes require the "imprimi potest" ("it can be printed") of their major superior to publish books on matters of religion or morals.


title: Index Librorum Prohibitorum

text: Some of the scientific theories contained in works in early editions of the "Index" have long been taught at Catholic universities. For example, the general prohibition of books advocating heliocentrism was removed from the "Index" in 1758, but two Franciscan mathematicians had published an edition of Isaac Newton's "Principia Mathematica" (1687) in 1742, with commentaries and a preface stating that the work assumed heliocentrism and could not be explained without it. A work of the Italian Catholic priest and philosopher Antonio Rosmini-Serbati was on the "Index", but he was beatified in 2007. Some have argued that the developments since the abolition of the "Index" signify "the loss of relevance of the Index in the 21st century."


title: Index Librorum Prohibitorum

text: J. Martínez de Bujanda's "Index Librorum Prohibitorum, 1600–1966" lists the authors and writings in the successive editions of the "Index", while Miguel Carvalho Abrantes's "Why Did The Inquisition Ban Certain Books?: A Case Study from Portugal" tries to understand why certain books were forbidden based on a Portuguese edition of the "Index Librorum Prohibitorum" from 1581.


title: Index Librorum Prohibitorum

text: The historical context in which the "Index" appeared involved the early restrictions on printing in Europe. The refinement of moveable type and the printing press by Johannes Gutenberg circa 1440 changed the nature of book publishing, and the mechanism by which information could be disseminated to the public. Books, once rare and kept carefully in a small number of libraries, could be mass-produced and widely disseminated.


title: Index Librorum Prohibitorum

text: In the 16th century, both the churches and governments in most European countries attempted to regulate and control printing because it allowed for rapid and widespread circulation of ideas and information. The Protestant Reformation generated large quantities of polemical new writing by and within both the Catholic and Protestant camps, and religious subject-matter was typically the area most subject to control. While governments and church encouraged printing in many ways, which allowed the dissemination of Bibles and government information, works of dissent and criticism could also circulate rapidly. As a consequence, governments established controls over printers across Europe, requiring them to have official licenses to trade and produce books.


title: Index Librorum Prohibitorum

text: The early versions of the "Index" began to appear from 1529 to 1571. In the same time frame, in 1557 the English Crown aimed to stem the flow of dissent by chartering the Stationers' Company. The right to print was restricted to two universities and to the 21 existing printers in the city of London, which had between them 53 printing presses.


title: Index Librorum Prohibitorum

text: The French crown also tightly controlled printing, and the printer and writer Etienne Dolet was burned at the stake for atheism in 1546. The 1551 Edict of Châteaubriant comprehensively summarized censorship positions to date, and included provisions for unpacking and inspecting all books brought into France. The 1557 Edict of Compiègne applied the death penalty to heretics and resulted in the burning of a noblewoman at the stake. Printers were viewed as radical and rebellious, with 800 authors, printers and book dealers being incarcerated in the Bastille. At times, the prohibitions of church and state followed each other, e.g. René Descartes was placed on the Index in the 1660s and the French government prohibited the teaching of Cartesianism in schools in the 1670s.


title: Index Librorum Prohibitorum

text: The Copyright Act 1710 in Britain, and later copyright laws in France, eased this situation. Historian Eckhard Höffner claims that copyright laws and their restrictions acted as a barrier to progress in those countries for over a century, since British publishers could print valuable knowledge in limited quantities for the sake of profit. The German economy prospered in the same time frame since there were no restrictions.


title: Index Librorum Prohibitorum

text: The first list of the kind was not published in Rome, but in Catholic Netherlands (1529); Venice (1543) and Paris (1551) under the terms of the Edict of Châteaubriant followed this example. By mid-century, in the tense atmosphere of wars of religion in Germany and France, both Protestant and Catholic authorities reasoned that only control of the press, including a catalog of prohibited works, coordinated by ecclesiastic and governmental authorities could prevent the spread of heresy.


title: Index Librorum Prohibitorum

text: Paul F. Grendler (1975) discusses the religious and political climate in Venice from 1540 – 1605. There were many attempts to censor the Venetian press, which was one of the largest concentrations of printers at that time. Both church and government held to a belief in censorship, but the publishers continually pushed back on the efforts to ban books and shut down printing. More than once the index of banned books in Venice was suppressed or suspended because various people took a stand against it.


title: Index Librorum Prohibitorum

text: The first Roman "Index" was printed in 1557 under the direction of Pope Paul IV (1555–1559), but then withdrawn for unclear reasons. In 1559, a new index was finally published, banning the entire works of some 550 authors in addition to the individual proscribed titles: "The Pauline Index felt that the religious convictions of an author contaminated all his writing." The work of the censors was considered too severe and met with much opposition even in Catholic intellectual circles; after the Council of Trent had authorised a revised list prepared under Pope Pius IV, the so-called "Tridentine Index" was promulgated in 1564; it remained the basis of all later lists until Pope Leo XIII, in 1897, published his "Index Leonianus".


title: Index Librorum Prohibitorum

text: The blacklisting of some Protestant scholars even when writing on subjects a modern reader would consider outside the realm of dogma meant that, unless they obtained a dispensation, obedient Catholic thinkers were denied access to works including: botanist Conrad Gesner's "Historiae animalium"; the botanical works of Otto Brunfels; those of the medical scholar Janus Cornarius; to Christoph Hegendorff or Johann Oldendorp on the theory of law; Protestant geographers and cosmographers like Jacob Ziegler or Sebastian Münster; as well as anything by Protestant theologians like Martin Luther, John Calvin or Philipp Melanchthon. Among the inclusions was the Libri Carolini, a theological work from the 9th century court of Charlemagne, which was published in 1549 by Bishop Jean du Tillet and which had already been on two other lists of prohibited books before being inserted into the Tridentine Index.


title: Index Librorum Prohibitorum

text: In 1571, a special congregation was created, the Sacred Congregation of the Index, which had the specific task to investigate those writings that were denounced in Rome as being not exempt of errors, to update the list of Pope Pius IV regularly and also to make lists of required corrections in case a writing was not to be condemned absolutely but only in need of correction; it was then listed with a mitigating clause (e.g., "donec corrigatur" (forbidden until corrected) or "donec expurgetur" (forbidden until purged)).


title: Index Librorum Prohibitorum

text: Several times a year, the congregation held meetings. During the meetings, they reviewed various works and documented those discussions. In between the meetings was when the works to be discussed were thoroughly examined, and each work was scrutinized by two people. At the meetings, they collectively decided whether or not the works should be included in the Index. Ultimately, the pope was the one who had to approve of works being added or removed from the Index. It was the documentation from the meetings of the congregation that aided the pope in making his decision.


title: Index Librorum Prohibitorum

text: This sometimes resulted in very long lists of corrections, published in the "Index Expurgatorius", which was cited by Thomas James in 1627 as "an invaluable reference work to be used by the curators of the Bodleian Library when listing those works particularly worthy of collecting". Prohibitions made by other congregations (mostly the Holy Office) were simply passed on to the Congregation of the Index, where the final decrees were drafted and made public, after approval of the Pope (who always had the possibility to condemn an author personally—there are only a few examples of such condemnation, including those of Lamennais and Hermes).


title: Index Librorum Prohibitorum

text: An update to the Index was made by Pope Leo XIII, in the 1897 apostolic constitution Officiorum ac Munerum, known as the "Index Leonianus". Subsequent editions of the Index were more sophisticated; they graded authors according to their supposed degree of toxicity, and they marked specific passages for expurgation rather than condemning entire books.


title: Index Librorum Prohibitorum

text: The Sacred Congregation of the Inquisition of the Roman Catholic Church later became the Holy Office, and since 1965 has been called the Congregation for the Doctrine of the Faith. The Congregation of the Index was merged with the Holy Office in 1917, by the Motu Proprio "Alloquentes Proxime" of Pope Benedict XV; the rules on the reading of books were again reelaborated in the new "Codex Iuris Canonici". From 1917 onward, the Holy Office (again) took care of the Index.


title: Index Librorum Prohibitorum

text: While individual books continued to be forbidden, the last edition of the Index to be published appeared in 1948. This 20th edition contained 4,000 titles censored for various reasons: heresy, moral deficiency, sexual explicitness, and so on. That some atheists, such as Schopenhauer and Nietzsche, were not included was due to the general (Tridentine) rule that heretical works ("i.e.", works that contradict Catholic dogma) are ipso facto forbidden. Some important works are absent simply because nobody bothered to denounce them. Many actions of the congregations were of a definite political content. Among the significant listed works of the period was the Nazi philosopher Alfred Rosenberg's "Myth of the Twentieth Century" for scorning and rejecting "all dogmas of the Catholic Church, indeed the very fundamentals of the Christian religion".


title: Index Librorum Prohibitorum

text: On 7 December 1965, Pope Paul VI issued the Motu Proprio "Integrae servandae" that reorganized the Holy Office as the "Sacred Congregation for the Doctrine of the Faith". The Index was not listed as being a part of the newly constituted congregation's competence, leading to questioning whether it still was. This question was put to Cardinal Alfredo Ottaviani, pro-prefect of the congregation, who responded in the negative. The Cardinal also indicated in his response that there was going to be a change in the Index soon.


title: Index Librorum Prohibitorum

text: A June 1966 Congregation for the Doctrine of the Faith notification announced that, while the "Index" maintained its moral force, in that it taught Christians to beware, as required by the natural law itself, of those writings that could endanger faith and morality, it no longer had the force of ecclesiastical positive law with the associated penalties.


title: Index Librorum Prohibitorum

text: The "Index" was not simply a reactive work. Roman Catholic authors had the opportunity to defend their writings and could prepare a new edition with necessary corrections or deletions, either to avoid or to limit a ban. Pre-publication censorship was encouraged.


title: Index Librorum Prohibitorum

text: The "Index" was enforceable within the Papal States, but elsewhere only if adopted by the civil powers, as happened in several Italian states. Other areas adopted their own lists of forbidden books. In the Holy Roman Empire book censorship, which preceded publication of the "Index", came under control of the Jesuits at the end of the 16th century, but had little effect, since the German princes within the empire set up their own systems. In France it was French officials who decided what books were banned and the Church's "Index" was not recognized. Spain had its own "Index Librorum Prohibitorum et Expurgatorum", which corresponded largely to the Church's, but also included a list of books that were allowed once the forbidden part (sometimes a single sentence) was removed or "expurgated".


title: Index Librorum Prohibitorum

text: On 14 June 1966, the Congregation for the Doctrine of the Faith responded to inquiries it had received regarding the continued moral obligation concerning books that had been listed in the Index. The response spoke of the books as examples of books dangerous to faith and morals, all of which, not just those once included in the Index, should be avoided regardless of the absence of any written law against them. The Index, it said, retains its moral force "inasmuch as" ("quatenus") it teaches the conscience of Christians to beware, as required by the natural law itself, of writings that can endanger faith and morals, but it (the Index of Forbidden Books) no longer has the force of ecclesiastical law with the associated censures.


title: Index Librorum Prohibitorum

text: The congregation thus placed on the conscience of the individual Christian the responsibility to avoid all writings dangerous to faith and morals, while at the same time abolishing the previously existing ecclesiastical law and the relative censures, without thereby declaring that the books that had once been listed in the various editions of the Index of Prohibited Books had become free of error and danger.


title: Index Librorum Prohibitorum

text: In a letter of 31 January 1985 to Cardinal Giuseppe Siri, regarding the book "The Poem of the Man-God", Cardinal Joseph Ratzinger (then Prefect of the Congregation, who later became Pope Benedict XVI), referred to the 1966 notification of the Congregation as follows: "After the dissolution of the Index, when some people thought the printing and distribution of the work was permitted, people were reminded again in "L'Osservatore Romano" (15 June 1966) that, as was published in the "Acta Apostolicae Sedis" (1966), the Index retains its moral force despite its dissolution. A decision against distributing and recommending a work, which has not been condemned lightly, may be reversed, but only after profound changes that neutralize the harm which such a publication could bring forth among the ordinary faithful."


title: Index Librorum Prohibitorum

text: The content of the Index Librorum Prohibitorum saw deletions as well as additions over the centuries. Writings by Antonio Rosmini-Serbati were placed on the Index in 1849 but were removed by 1855, and Pope John Paul II mentioned Rosmini's work as a significant example of "a process of philosophical enquiry which was enriched by engaging the data of faith". The 1758 edition of the Index removed the general prohibition of works advocating heliocentrism as a fact rather than a hypothesis.


title: Index Librorum Prohibitorum

text: Noteworthy figures on the Index include Simone de Beauvoir, Nicolas Malebranche, Jean-Paul Sartre, Michel de Montaigne, Voltaire, Denis Diderot, Victor Hugo, Jean-Jacques Rousseau, André Gide, Nikos Kazantzakis, Emanuel Swedenborg, Baruch Spinoza, Desiderius Erasmus, Immanuel Kant, David Hume, René Descartes, Francis Bacon, Thomas Browne, John Milton, John Locke, Nicolaus Copernicus, Galileo Galilei, Blaise Pascal, and Hugo Grotius. The first woman to be placed on the list was Magdalena Haymairus in 1569, who was listed for her children's book "Die sontegliche Episteln über das gantze Jar in gesangsweis gestellt" ("Sunday Epistles on the whole Year, put into hymns"). Other women include Anne Askew, Olympia Fulvia Morata, Ursula of Munsterberg (1491–1534), Veronica Franco, and Paola Antonia Negri (1508–1555).


title: Index Librorum Prohibitorum

text: In many cases, an author's "opera omnia" (complete works) were forbidden. However, the Index stated that the prohibition of someone's "opera omnia" did not preclude works that were not concerned with religion and were not forbidden by the general rules of the Index. This explanation was omitted in the 1929 edition, which was officially interpreted in 1940 as meaning that "opera omnia" covered all the author's works without exception.


title: Index Librorum Prohibitorum

text: Cardinal Ottaviani stated in April 1966 that there was too much contemporary literature and the Sacred Congregation for the Doctrine of the Faith could not keep up with it.


title: Shades of purple

text: However, the meaning of the term purple is not well defined. There is confusion about the meaning of the terms purple and violet even among native speakers of English. Many native speakers of English in the United States refer to the blue-dominated spectral color beyond blue as purple, but the same color is referred to as violet by many native English speakers in the United Kingdom. The full range of colors between red and blue is referred to by the term purple in some British authoritative texts, whereas the same range of colors is referred to by the term violet in some other texts.


title: Shades of purple

text: The confusion about the range of meanings of the terms violet and purple is even larger when including other languages and historical texts.


title: Shades of purple

text: Since this Wikipedia page contains contributions from authors from different countries and different native languages, this Wikipedia page is likely to be not consistent in the use of the color terms purple and violet.


title: Shades of purple

text: In formal color theory, "purple" colors often refer to the colors on the line of purples on the CIE chromaticity diagram (or colors that can be derived from colors on the line of purples), i.e., any color between red and violet, not including either red or violet themselves.


title: Shades of purple

text: "See also under Purple#In art, history and fashion the section "In prehistory and the ancient world: Tyrian purple" "


title: Shades of purple

text: "Tyrian purple" is the contemporary English name of the color that in Latin is denominated ""purpura"". Other contemporary English names for "purpura" are "imperial purple" and "royal purple". The English name "purple" itself originally denominated the specific color "purpura". "Purpura" is the color of a dye extracted from a mollusk found on the shores of the city of Tyre in ancient Phoenicia (contemporarily in Lebanon), which color in classical antiquity was a symbol of royalty and political authority because only the very wealthy could afford it, including the Roman Emperors. Therefore, Tyrian purple was also denominated "imperial purple".


title: Shades of purple

text: Tyrian purple may have been discovered as early as during the Minoan civilization. Alexander the Great, when giving imperial audiences as the Emperor of Macedonia; the Emperor of the Seleucid Empire; and the Kings of Ptolemaic Egypt all wore Tyrian purple. The imperial robes of Roman emperors were of Tyrian purple trimmed in metallic gold thread. The badge of office of a Roman Senator was a stripe of Tyrian purple on his white toga. Tyrian purple was continued in use by the Emperors of the Eastern Roman Empire until its final collapse in 1453.


title: Shades of purple

text: The tone of Tyrian purple displayed above is that tone of Tyrian purple which was the color of "clotted blood", which was considered the tone having the most prestige in ancient Greece and Rome, as recorded by Pliny the Elder. However, the actual tone varied depending on how the dye was formulated. Lesser royal houses that wanted to economize could mix Tyrian purple dye with the much less expensive indigo to create a color closer to violet.


title: Shades of purple

text: Han purple is a type of artificial pigment found in China between 500 BC and AD 220. It was used in the decoration of the Terracotta Army.


title: Shades of purple

text: Mauveine was first named in 1856. Chemist Sir William Henry Perkin, then eighteen, was attempting to create artificial quinine. An unexpected residue caught his eye, which turned out to be the first aniline dye—specifically, "Perkin's mauve" or "mauveine" is sometimes called "aniline purple". Perkin was so successful in recommending his discovery to the dyestuffs industry that his biography by Simon Garfield is titled "Mauve". As mauveine faded easily, our contemporary understanding of mauve is as a lighter, less saturated color than it was originally known.


title: Shades of purple

text: "Mauveine" was named after the mauve colored mallow flower, even though it is a much deeper tone of purple than mauve. The term "Mauve" in the late 19th century could refer to either the deep, rich color of the dye or the light color of the flower. Mauve (meaning Mauveine) came into great vogue when in 1862 Queen Victoria appeared at the Royal Exhibition in a mauve silk gown—dyed with mauveine. By 1890, this color had become so pervasive in fashion that author Thomas Beer used it in the title of his book about the 1890s, "The Mauve Decade".


title: Shades of purple

text: In some parts of the world, 'Royal purple' (shown above) or the dark violet color known as "generic purple" is the common layman's idea of purple, but these color terms carry different meanings in different parts of the world. Even among modern native speakers of English there is confusion about the terms purple and violet. In the United Kingdom, many native speakers of English refer to the blue-dominated spectral color beyond blue as violet, but this color is called purple by many speakers in the United States.


title: Shades of purple

text: In some texts the term violet refers to any color between red and blue. However, there are also authoritative texts from the United Kingdom in which this same range of colors is referred to by the term purple.


title: Shades of purple

text: When including languages other than English, and epochs other than the modern period, the uncertainty about the meanings of the color terms violet and purple is even larger. Since this Wikipedia page contains contributions from authors from different countries and different native languages, it is likely to be not consistent in the use of the color terms violet and purple.


title: Shades of purple

text: Artists that happen to follow Munsell color system (introduced in 1905 and used since 1930 by a large number of artists in the United States, but by much fewer artists outside the US), may regard purple as being synonymous with the red-violet color, represented by the web color medium violet red. Munsell included purple as a color hue in his color system, but he did not do so for violet as he did not need it as a label for his system (just like the hue term orange is not used in Munsell's system). If defined as blue-dominated colors between blue and red, violet colors in Munsell's system would be classified as having the 7.5PB and 10.0PB hue, which is confirmed in visual experiments


title: Shades of purple

text: The truly purple color, defined as being within the range of the red-dominated colors between red and blue, is sometimes confusingly labeled as red-violet color, or more correctly artist's purple. It is the pigment color that would be on a pigment color color wheel between pigment violet and pigment (process) magenta. In the Munsell color system, this color at its maximum chroma of 12 is called Red-Purple, or more specifically Munsell 5RP.


title: Shades of purple

text: Artists' pigments and colored pencils labeled as purple are typically colored the red-violet color. On an RYB color wheel, the so-called red-violet color is the color between red and violet.


title: Shades of purple

text: This color, electric purple, is precisely halfway between violet and magenta and thus fits the artistic definition of purple.


title: Shades of purple

text: Using additive colors such as those on computer screens, it is possible to create a much brighter purple than with pigments where the mixing subtracts frequencies from the component primary colors. The equivalent color on a computer to the pigment color red-violet shown above would be this electric purple, i.e. the much brighter purple you can see reproduced on the screen of a computer. This color is pure purple conceived as computer artists conceive it, as the color on the color wheel halfway between color wheel violet and electric magenta. Thus, electric purple is the purest and brightest purple that it is possible to display on a computer screen. Its RGB code is (191, 0, 255).


title: Shades of purple

text: An old name for this color, used by Robert Ridgway in his 1912 book on color nomenclature, "Color Standards and Color Nomenclature", is true purple.


title: Shades of purple

text: This purple used in HTML and CSS actually is deeper and has a more reddish hue (#800080) than the X11 color purple shown below as "purple" (X11 color) (#A020F0), which is bluer and brighter. This is one of the very few clashes between web and X11 colors.


title: Shades of purple

text: This color may be called HTML/CSS purple. It seems likely that this color was chosen as the web color purple because its hue is exactly halfway between red and blue and its value is exactly halfway between white and black.


title: Shades of purple

text: A traditional name sometimes used for this tone of purple is patriarch. The first recorded use of "patriarch" as a color name in English was in 1925.


title: Shades of purple

text: The color purple, as defined in the X11 color names in 1987, is brighter and bluer than the HTML/CSS web color purple shown above as "purple (HTML/CSS color)". This is one of the very few clashes between web and X11 colors.


title: Shades of purple

text: The traditional name for this tone of purple is veronica. The first recorded use of "veronica" as a color name in English was in 1919.


title: Shades of purple

text: This color is defined as purple in the Munsell color system (Munsell 5P). The "Munsell color system" is a color space that specifies colors based on three color dimensions: hue, value (lightness), and chroma (color purity), spaced uniformly in three dimensions in the elongated oval at an angle shaped Munsell color solid according to the logarithmic scale which governs human perception. In order for all the colors to be spaced uniformly, it was found necessary to use a color wheel with five primary colors—red, yellow, green, blue, and purple.


title: Shades of purple

text: The Munsell colors displayed are only approximate as they have been adjusted to fit into the sRGB gamut.


title: Shades of purple

text: Mauve (rhymes with "grove"; from the French form of "Malva" "mallow") is a pale purple. Mauve is named after the mallow flower. Another name for the color is mallow with the first recorded use of "mallow" as a color name in English in 1611.


title: Shades of purple

text: The color thistle is associated with Scotland because the thistle is the national flower of Scotland and Scotland's highest state decoration is the Order of the Thistle.


title: Shades of purple

text: The color orchid is a bright rich purple. The name 'orchid' originates from the flowers of some species of the vast orchid flower family, such as "Laelia furfuracea" and "Ascocentrum pusillum", which have petals of this color.


title: Shades of purple

text: The color heliotrope is a brilliant tone of purple; it is a pink-purple tint that is a representation of the color of the heliotrope flower.


title: Shades of purple

text: The pure essence of purple was approximated in pigment in the late 1960s by mixing fluorescent magenta and fluorescent blue pigments together to make "fluorescent purple" to use in psychedelic black light paintings. This tone of purple was very popular among hippies and was the favorite color of Jimi Hendrix. Thus it is called psychedelic purple. Psychedelic purple is the color halfway between electric purple and magenta.


title: Shades of purple

text: In the 1980s, there was a "Jimi Hendrix Museum" in a Victorian house on the east side of Central Avenue one half block south of Haight Street in the Haight-Ashbury neighborhood of San Francisco which was painted this color.


title: Shades of purple

text: Another name for this color is phlox, as it is the color of the phlox flower. The first recorded use of "phlox" as a color name in English was in 1918.


title: Shades of purple

text: The color mulberry is a representation of the color of mulberry jam or pie. This was a Crayola crayon color from 1958 to 2003.


title: Shades of purple

text: Pearly purple is one of the colors in the special set of metallic colored Crayola crayons called Silver Swirls, the colors of which were formulated by Crayola in 1990.


title: Shades of purple

text: Northwestern Purple is the official color of Northwestern University. Additionally, there are shades and tints that are variations of the base color. Northwestern Purple is a custom ink color and can no longer be referenced by a Pantone number.


title: Shades of purple

text: For printed material, purple (Pantone #268+) is the official school color of Kansas State University. Traditionally, the school has referred to this darker and bluer shade as Royal Purple. [compare with ]


title: Shades of purple

text: For the web, #512888 is the official color, even though that hex triplet is not a direct conversion from Pantone 268+.


title: Shades of purple

text: The color pomp and power is not found in the 1930 first edition of the "Dictionary of Color" by Maerz and Paul, but it is found in the second edition of 1950.


title: Shades of purple

text: The for pomp and power are identical to french lilac, first recorded as a color name in English in 1814.


title: Shades of purple

text: The color name Mardi Gras has been in use since 2001 when the Xona.com Color List was first promulgated.


title: Shades of purple

text: The color name eminence, used since the 1800s, has been in modern use for this color since 2001 when the Xona.com Color List was first promulgated.


title: Shades of purple

text: The pansy flower has varieties that exhibit three different colors: "pansy" (a color between indigo and violet), "pansy pink", and pansy purple.


title: Shades of purple

text: Palatinate is a color (a pale shade of violet) associated with the University of Durham (and with Newcastle University Medical School, this being the former medical school of Durham University.) A separate color, 'Palatinate Blue', is derived from the Coat of Arms of County Durham. The name 'Palatinate' in both instances alludes to the historic status of Durham as a County Palatine.


title: Gull

text: Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century, most gulls were placed in the genus "Larus", but that arrangement is now considered polyphyletic, leading to the resurrection of several genera. An older name for gulls is mews, which is cognate with German "Möwe", Danish "måge", Swedish "mås", Dutch "meeuw", Norwegian "måke"/"måse" and French "mouette", and can still be found in certain regional dialects.


title: Gull

text: Gulls are typically medium to large in size, usually grey or white, often with black markings on the head or wings. They typically have harsh wailing or squawking calls; stout, longish bills; and webbed feet. Most gulls are ground-nesting carnivores which take live food or scavenge opportunistically, particularly the "Larus" species. Live food often includes crustaceans, molluscs, fish and small birds. Gulls have unhinging jaws which allow them to consume large prey. Gulls are typically coastal or inland species, rarely venturing far out to sea, except for the kittiwakes. The large species take up to four years to attain full adult plumage, but two years is typical for small gulls. Large white-headed gulls are typically long-lived birds, with a maximum age of 49 years recorded for the herring gull.


title: Gull

text: Gulls nest in large, densely packed, noisy colonies. They lay two or three speckled eggs in nests composed of vegetation. The young are precocial, born with dark mottled down and mobile upon hatching. Gulls are resourceful, inquisitive, and intelligent, the larger species in particular, demonstrating complex methods of communication and a highly developed social structure. For example, many gull colonies display mobbing behavior, attacking and harassing predators and other intruders. Certain species have exhibited tool-use behavior, such as the herring gull, using pieces of bread as bait with which to catch goldfish, for example. Many species of gulls have learned to coexist successfully with humans and have thrived in human habitats. Others rely on kleptoparasitism to get their food. Gulls have been observed preying on live whales, landing on the whale as it surfaces to peck out pieces of flesh.


title: Gull

text: Gulls range in size from the little gull, at and , to the great black-backed gull, at and . They are generally uniform in shape, with heavy bodies, long wings, and moderately long necks. The tails of all but three species are rounded; the exceptions being Sabine's gull and swallow-tailed gulls, which have forked tails, and Ross's gull, which has a wedge-shaped tail. Gulls have moderately long legs, especially when compared to the similar terns, with fully webbed feet. The bill is generally heavy and slightly hooked, with the larger species having stouter bills than the smaller species. The bill colour is often yellow with a red spot for the larger white-headed species and red, dark red or black in the smaller species.


title: Gull

text: The gulls are generalist feeders. Indeed, they are the least specialised of all the seabirds, and their morphology allows for equal adeptness in swimming, flying, and walking. They are more adept walking on land than most other seabirds, and the smaller gulls tend to be more manoeuvrable while walking. The walking gait of gulls includes a slight side to side motion, something that can be exaggerated in breeding displays. In the air, they are able to hover and they are also able to take off quickly with little space.


title: Gull

text: The general pattern of plumage in adult gulls is a white body with a darker mantle; the extent to which the mantle is darker varies from pale grey to black. A few species vary in this, the ivory gull is entirely white, and some like the lava gull and Heermann's gull have partly or entirely grey bodies. The wingtips of most species are black, which improves their resistance to wear and tear, usually with a diagnostic pattern of white markings. The head of a gull may be covered by a dark hood or be entirely white. The plumage of the head varies by breeding season; in nonbreeding dark-hooded gulls, the hood is lost, sometimes leaving a single spot behind the eye, and in white-headed gulls, nonbreeding heads may have streaking.


title: Gull

text: The gulls have a worldwide cosmopolitan distribution. They breed on every continent, including the margins of Antarctica, and are found in the high Arctic as well. They are less common on tropical islands, although a few species do live on islands such as the Galapagos and New Caledonia. Many species breed in coastal colonies, with a preference for islands, and one species, the grey gull, breeds in the interior of dry deserts far from water. Considerable variety exists in the family and species may breed and feed in marine, freshwater, or terrestrial habitats.


title: Gull

text: Most gull species are migratory, with birds moving to warmer habitats during the winter, but the extent to which they migrate varies by species. Some migrate long distances, like Franklin's gull, which migrates from Canada to wintering grounds in the south of South America. Other species move much shorter distances and may simply disperse along the coasts near their breeding sites.


title: Gull

text: A big influence on non-breeding gull distribution are food patches. Human fisheries especially have an impact since they often provide an abundant and predictable food resource. Looking at two species of gulls dependent on human fisheries, Audouin ("Ichthyaetus audouinii") and black-backed gulls ("Larus fuscus)", their breeding distributions (especially the black-backed gull) was heavily impacted by human fishing discards and fishing ports.


title: Gull

text: Looking further at environmental drivers that structure bird habitat and distribution are human and climate impacts. Looking at waterbird distribution in wetlands, changes in salinity, water depth, water body isolation and hydroperiod altered bird community structure in both a species and guild specific way. Gulls in particular had high associations with salinity levels, being the main environmental predictor for waterbird assemblage.


title: Gull

text: Charadriiform birds drink salt water, as well as fresh water, as they possess exocrine glands located in supraorbital grooves of the skull by which salt can be excreted through the nostrils to assist the kidneys in maintaining electrolyte balance.


title: Gull

text: Gulls are highly adaptable feeders that opportunistically take a wide range of prey. The food taken by gulls includes fish and marine and freshwater invertebrates, both alive and already dead, terrestrial arthropods and invertebrates such as insects and earthworms, rodents, eggs, carrion, offal, reptiles, amphibians, plant items such as seeds and fruit, human refuse, and even other birds. No gull species is a single-prey specialist, and no gull species forages using only a single method. The type of food depends on circumstances, and terrestrial prey such as seeds, fruit, and earthworms are more common during the breeding season while marine prey is more common in the nonbreeding season when birds spend more time on large bodies of water.


title: Gull

text: In addition to taking a wide range of prey, gulls display great versatility in how they obtain prey. Prey can be obtained in the air, on water, or on land. In the air, a number of hooded species are able to hawk insects on the wing; larger species perform this feat more rarely. Gulls on the wing also snatch items both off water and off the ground, and over water they also plunge-dive to catch prey. Again, smaller species are more manoeuvrable and better able to hover-dip fish from the air. Dipping is also common when birds are sitting on the water, and gulls may swim in tight circles or foot paddle to bring marine invertebrates up to the surface. Food is also obtained by searching the ground, often on the shore among sand, mud or rocks. Larger gulls tend to do more feeding in this way. In shallow water gulls may also engage in foot paddling. One method of obtaining prey involves dropping heavy shells of clams and mussels onto hard surfaces. Gulls may fly some distance to find a suitable surface on which to drop shells, and apparently a learned component to the task exists, as older birds are more successful than younger ones. While overall feeding success is a function of age, the diversity in both prey and feeding methods is not. The time taken to learn foraging skills may explain the delayed maturation in gulls.


title: Gull

text: Gulls have only a limited ability to dive below the water to feed on deeper prey. To obtain prey from deeper down, many species of gulls feed in association with other animals, where marine hunters drive prey to the surface when hunting. Examples of such associations include four species of gulls feeding around plumes of mud brought to the surface by feeding grey whales, and also between orcas (largest dolphin species) and kelp gulls (and other seabirds).


title: Gull

text: Looking at the effect of humans on gull diet, overfishing of target prey such as sardines have caused a shift in diet and behavior. Analysis of yellow-legged gull's ("Larus michahellis)" pellets off the northwest coast of Spain revealed a shift from a sardine to crustacean-based diet. This shift was linked to higher fishing efficiency and thus overall fish stock depletion. Lastly, closure of nearby open-air landfills limited food availability for the gulls, furthering creating a stress on their shift in diet. Between the years of 1974–1994, yellow-legged gull populations in Berlenga Island, Portugal, increased from 2600 to 44,698 individuals. Analyzing both adult and chick remains, researchers found a mixture of both natural prey and human refuse. The gulls relied substantially on the Henslow's swimming crab ("Polybius henslowii"). Yet, in times when local prey availability is low, the gulls shift to human-related food. These temporal shifts from a marine to terrestrial prey highlight the resilience adult gulls have and their ability to keep chick condition consistent. Human disturbance has also shown to have an effect on gull breeding, in which hatching failure is directly proportional to the amount of disturbance in a given plot. Certain gull breeds have been known to feast on the eye balls of baby seals, and directly pilfer milk from the elephant seal's teat.


title: Gull

text: Gulls are monogamous and colonial breeders that display mate fidelity that usually lasts for the life of the pair. Divorce of mated pairs does occur, but it apparently has a social cost that persists for a number of years after the break-up. Gulls also display high levels of site fidelity, returning to the same colony after breeding there once and even usually breeding in the same location within that colony. Colonies can vary from just a few pairs to over a hundred thousand pairs, and may be exclusive to that gull species or shared with other seabird species. A few species nest singly, and single pairs of band-tailed gulls may breed in colonies of other birds. Within colonies, gull pairs are territorial, defending an area of varying size around the nesting site from others of their species. This area can be as large as a 5-m radius around the nest in the herring gull to just a tiny area of cliff ledge in the kittiwakes.


title: Gull

text: Most gulls breed once a year and have predictable breeding seasons lasting for three to five months. Gulls begin to assemble around the colony for a few weeks prior to occupying the colony. Existing pairs re-establish their pair-bonds, and unpaired birds begin courting. Birds then move back into their territories and new males establish new territories and attempt to court females. Gulls defend their territories from rivals of both sexes through calls and aerial attacks.


title: Gull

text: Nest building is also part of the pair-bonding. Gull nests are usually mats of herbaceous matter with a central nest cup. Nests are usually built on the ground, but a few species build nests on cliffs, including the kittiwakes, which almost always nest in such habitats, and in some cases in trees, and high places like Bonaparte's gulls. Species that nest in marshes must construct a nesting platform to keep the nest dry, particularly in species that nest in tidal marshes. Both sexes gather nesting material and build the nest, but the division of labour is not always exactly equal. In coastal towns, many gulls nest on rooftops and can be observed by nearby human residents.