The number 13 is synonymous with bad luck. It's considered unlucky to have 13 guests at a dinner party, many buildings don't have a 13th floor and most people avoid getting married or buying a house on a day marked by this dreaded number. Particularly superstitious folks even avoid driving on Friday the 13th. 
 
 But is there any statistical proof to support the notion that Friday the 13th — or even just the number 13 itself — is unlucky? 
 
 "No data exists, and will never exist, to confirm that the number 13 is an unlucky number," said Igor Radun of the Human Factors and Safety Behavior Group at the University of Helsinki's Institute of Behavioural Sciences in Finland. "There is no reason to believe that any number would be lucky or unlucky." 
 
 Radun might very well be correct, but there are a few bits of scientific research that have given superstitious people a little more cause for concern, even if the scientists who performed the work aren't alarmed by their findings. [15 Weird Things Humans Do Every Day, and Why ] 
 
 For starters, in a 1993 study published in the British Medical Journal, researchers analyzed the traffic flow and number of injuries from car accidents on the southern section of London's M25 motorway during the five months that the 13th fell on a Friday between 1990 and 1992. 
 
 They compared these numbers to data collected on Friday the 6th of the same months, and found that although there are consistently fewer vehicles on the road during the 13th — possibly as a result of superstitious people choosing not to drive that day, the researchers proposed — "the risk of hospital admission as a result of a transport accident may be increased by as much as 52 percent" on the 13th. 
 
 But before triskaidekaphobics, or those who fear the number 13, say "I told you so," it should be noted that although the data were authentic, the authors didn't mean for their conclusions to be taken seriously. 
 
 "It's quite amusing and written with tongue firmly in cheek," said Robert Luben, a researcher at the school of clinical medicine at the University of Cambridge and one of the study's authors. "It was written for the Christmas edition of the British Medical Journal, which usually carries fun or spoof articles." 
 
 Many people took the study at face value, however, and it continues to be cited as valid evidence regarding the misfortune of both the number 13 and Friday the 13th . 
 
 "(Some people) clearly didn't understand that the paper was just a bit of fun and not to be taken seriously," Luben told Life's Little Mysteries. "Many also assumed that the authors were 'believers.' I'm sure that most of these people hadn't read the paper, which suggests that people being superstitious affects their behavior." 
 
 Since the 1993 study, other studies have been written showing that it's just women who have more accidents on Friday the 13th , with further studies concluding that's actually not the case. Other research results attempting to measure just how unlucky the number 13 is have been mixed. 
 
 For example, in 2005, the United Kingdom newspaper The Telegraph analyzed the winning lottery balls dating back to when the UK National Lottery began in 1994. They found that the number 13 was the unluckiest ball, because it was drawn a total of 120 times since 1994, compared with the luckiest ball, number 38, which was drawn a total of 182 times. But, "of course, there is no way of predicting which balls will be luckiest in the future," the article cautions. 
 
 Not everyone has found similar patterns. 
 
 "Unfortunately, most of studies dealing with Friday the 13th and the number 13 are solely focused on statistical data, such as accident data, stock exchange data, etc., without any attempt to establish a 'direct' relationship between belief, or superstition, and behavior," said Radun, who is co-author of the 2004 study "Females Do Not Have More Injury Road Accidents on Friday the 13th," which was published in the journal BMC Public Health. "Therefore, it is not surprising that contradictory results may occur … In our study, we did not find that either women or men have more injury road accidents on Friday the 13th compared to previous and following Fridays." [Superstitions Bring Real Luck, Study Reveals ] 
 
 Luben agrees that studies about statistics surrounding the number 13 should acknowledge how people's superstitions influence how they act. He wrote in his study that "superstitions affect behavior in all cultures in all parts of the world in some form or other." So whether you vow to never play the number 13 in a lottery or declare that 13 is your lucky number just to go against the grain, the stigma surrounding the number still influenced your decision. 
 
 "There are no lucky or unlucky numbers; they exist only in our heads – or in the heads of some of us – and they might become lucky or unlucky only if we make them as such," Radun said. 
 
 But many triskaidekaphobics, who count author Stephen King and former president Franklin Roosevelt among their ranks, don't need statistical evidence or hard facts to back up their conviction that the number is truly cursed. As with any superstition, no matter how irrational it may be, some people will still choose to believe in it. 
 
 Follow Life's Little Mysteries on Twitter @llmysteries. We're also on Facebook & Google+. ||||| Does Friday the 13th freak you out? If so, hold on to your rabbit's foot extra tight, because there are three of these supposedly unlucky dates in 2012, though perhaps luckily, this Friday (July 13) is the last of them. Though, there's always some fear to be had next year, 2013. 
 
 Read on for 13 strange facts about this day of superstition. 
 
 1. This year is a special one for Friday the 13ths: There are three of them: Jan. 13, April 13 and July 13. The freaky thing? The dates fall exactly 13 weeks apart. That hasn't happened since 1984. 
 
 2. If that scares you, you may have paraskavedekatriaphobia (also known as friggatriskaidekaphobia). Those are the scientific terms for fear of Friday the 13th. Triskaidekaphobia is fear of the number 13. 
 
 3. It's not clear when or why Friday the 13th became associated with bad luck. The association may be biblical, given that the 13th guest at the Last Supper betrayed Jesus. His crucifixion was the next day, apparently a Friday. Or maybe 13 suffers from coming after the more-pleasing number 12, which gets to number the months, the days of Christmas and even the eggs in a dozen. (There are also 12 signs of the zodiac, 12 gods of Olympus, 12 labors of Hercules, 12 tribes of Israel and 12 apostles of Jesus.) 
 
 4. Whatever the reason, fear of 13 has spread far and wide: Hotels and hospitals often skip the 13th floor, and even airports quietly omit gate 13 sometimes. 
 
 5. The next year in which we'll have three Friday the 13ths is 2015. They'll fall in February, March and November. 
 
 6. If you think your Friday the 13th is likely to be bad, be glad you aren't a 14th-century Knight Templar. On Oct. 13, 1307, officers of King Philip IV of France raided the homes of thousands of these Crusades warriors, imprisoning them on charges of illegal activities. Though the charges weren't proven, more than a hundred died of terrible torture, according to "Tales of the Knights Templar" (Warner Books, 1995). 
 
 7. Fittingly, director of psychological thrillers Alfred Hitchcock was born on the 13th — Friday, Aug. 13, 1999, would have been his 100th birthday. Perhaps aptly titled "Number 13," a film that was supposed to be Hitchcock's directorial debut never made it past the first few scenes and was shut down due to financial problems. He allegedly said the film wasn't very interesting. (Meanwhile, Fidel Castro was born on Friday the 13th, in August 1926.) 
 
 8. Why does the Friday the 13th superstition stick so firmly in our minds? According to Thomas Gilovich, who chairs the department of psychology at Cornell University, our brains are almost too good at making associations. 
 
 "If anything bad happens to you on Friday the 13th, the two will be forever associated in your mind, and all those uneventful days in which the 13th fell on a Friday will be ignored," Gilovich said in a statement. [13 Superstitions & Traditions Explained] 
 
 9. For pagans, 13 is actually a lucky number. It corresponds with the number of full moons in a year. 
 
 10. President Franklin D. Roosevelt is said to have avoided travel on the 13th day of any month, and would never host 13 guests at a meal. Napoleon and President Herbert Hoover were also triskaidekaphobic, with an abnormal fear of the number 13. 
 
 11. Mark Twain once was the 13th guest at a dinner party. A friend warned him not to go. "It was bad luck," Twain later told the friend. "They only had food for 12." Superstitious diners in Paris can hire a quatorzieme, or professional 14th guest. [13 Odd Occurrences on Friday the 13th] 
 
 12. Stock broker and author Thomas W. Lawson, in his 1907 novel "Friday the Thirteenth," wrote of a stockbroker's attempts to take down Wall Street on the unluckiest day of the month. Reportedly, stock brokers after this were as unlikely to buy or sell stocks on this unlucky day as they were to walk under a ladder, according to accounts of a 1925 New York Times article. 
 
 13. This fear of Friday the 13th can be serious business, according to the Stress Management Center and Phobia Institute in Asheville, N.C., which, among other things, offers therapy to help people overcome their fear of the freaky friday. Their estimates suggest hundreds of millions of dollars, up to $900 million are lost due to people's fear of flying or doing the business as usual that day, though that number isn't backed up with other estimates. 
 
 Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook. ||||| Though the summer wedding season may be at its peak, today will be especially quiet for wedding vendors like Lethal Rhythms, a company based in Atlanta that provides professional mix DJ services in the Southeast. 
 
 That's because couples are hesitant to begin their matrimony on Friday the 13th, leading many businesses to offer discounts to ease their superstitions. 
 
 In Photos: Myths and History of Friday the 13th 
 
 Kra Riddell, market manager for Lethal Rhythms, said she has no events planned today, not even an anniversary or birthday party. In fact, Riddell said, Friday the 13th seems to regularly affect general hospitality businesses in Atlanta. 
 
 "I think the Southeast is very superstitious," said Riddell, who has worked for the company since 2010. 
 
 Although there are plenty of client meetings scheduled today, the clubs and nightlife events for which Lethal Rhythms provides services also quiet down when Friday the 13th rolls around. 
 
 "It's very bare in the clubs. I feel like people stay inside," Riddell said. 
 
 Ridell recently became engaged, and though she is not superstitious she said she "definitely would not get married on Friday the 13th." 
 
 "I'm not a big believer in karma, but I don't want anything to help it," she said with a laugh. 
 
 Anja Winikka, site editor of wedding site TheKnot.com, said Friday the 13th is not "couples' wedding date of choice." 
 
 "Choosing a wedding date is important from the beginning and they want it to be special to them," she said. 
 
 Fridays are not as sought after as Saturdays for weddings, though Fridays and Sundays are becoming more popular as vendors offer discounts to couples who choose to wed on those off-peak days. 
 
 But Friday weddings appear to be significantly infrequent on Friday the 13th. 
 
 According to The Knot's annual weddings survey, there will be 2,845 weddings today, compared to 3,111 last Friday. There will be 4,190 next Friday, July 20 and 3,407 weddings on Friday, July 27. However, there will be a whopping 17,886 weddings on Saturday. 
 
 In April, when the last Friday the 13th occurred, the unpopularity of Friday the 13th was even more apparent. 
 
 On Friday, April 13, there were 1,764 weddings, only slightly higher than the Friday of the previous week, 1,449. That was Easter and Passover weekend, a typically unpopular wedding time. 
 
 By comparison, there were 3,329 weddings on Friday, April 20, and 2,303 on Friday, April 27. 
 
 Of note, April is not as popular for weddings and considered a "shoulder" month because it flanks the main season, Winikka said. 
 
 Jason Shukovsky, director of catering for The Crystal Plaza, a private mansion in Livingston, N.J., said Friday the 13ths are "a big more challenging to sell" so the company may offer a discount of 10 to 15 percent. 
 
 He said many clients take the discounted offer. 
 
 "We're a little pricier than some of our competition in the area. If we give them an opportunity to work a little more within their budget, it works out better for them," he said. "People are more bargain-conscious now, more than they have ever been, due to the economic times." 
 
 The company hosts about 370 events a year, one at a time, 300 of which are weddings, Shukovsky said. 
 
 Not all brides and grooms are swayed away from Friday the 13th because of superstition. 
 
 One couple intentionally chose to get married on a future Friday the 13th at The Crystal Plaza and will have a "skull and crossbones" theme. That date was already selected by another couple that was admittedly hesitant over the superstition around Friday the 13th. So Shukovsky offered that couple another Friday with a discount, which they gleefully accepted. 
 
 Sari Lindeman, sales manager at Bellagala, a full-service wedding boutique based in Minneapolis, said the company has eight weddings planned today, a "significant increase" in business compared to the corresponding Friday, July 15, last year. 
 
 "If they find the day they love and vendors are open to work with them, I think the Friday the 13th superstition goes out the window," Lindeman said. 
 
 Bellagala didn't offer deeper discounts on the three Friday the 13th dates this year compared to any other off-peak date. 
 
 One bride who chose Friday the 13th told Lindeman that she was leery at first out of concern about any superstitious guests. But in the end, she didn't allow it affect her final decision. 
 
 Bellgalla's staff isn't allowing superstition to affect its work either. Lindeman said the company is abuzz with the same excitement and energy as before any busy wedding weekend. 
 
 "As our profession, this is what we do day-in and day-out," she said. "It's not taken lightly because it's such an important day for our couples."
– Good news for those with paraskevidekatriaphobia: It's the last Friday the 13th of the year, and if you learn to say that word—meaning fear of Friday the 13th—you'll get rid of your fear, according to a superstition relayed by NPR. But is there any truth behind the fear? A study in the early 1990s suggests so: Researchers found that "the risk of hospital admission as a result of a transport accident may be increased by as much as 52%" on a Friday the 13th, according to Life's Little Mysteries. That study, however, was "written with tongue firmly in cheek," notes an author, although authentic data were used. Later studies have been mixed, with some data suggesting women experience more accidents on the date, and others rejecting the idea entirely. Ridiculous or not, the superstition certainly has real-world effects: Many avoid the date for weddings, prompting some wedding-related businesses to give Friday the 13th discounts, notes ABC News. And one stress-management group figures that up to $900 million may be lost because of people's avoidance of flying and other normal activities on the date, LiveScience reports.