Sampling Framework 
 
 We conducted a randomized survey of 3299 households from January 17 through February 24, 2018. The target sample of approximately 3000 households was calculated to detect a 50% increase in the annual mortality rate from a historic (September 20 through December 31) baseline rate of 8 per 1000,21 with 80% power at a significance level of 0.05. To ensure sampling of households across geographic regions, we stratified the population according to remoteness, defined according to the travel time to the nearest city with a population of at least 50,000 persons.22,23 We determined an average remoteness index for each of the 900 barrios (administrative units) by using population and road-network data from official government sources.24 Barrios were grouped into eight categories according to percentile from least remote (category 1) to most remote (category 8), and 13 barrios were randomly sampled from each category (Fig. S1 in the Supplementary Appendix, available with the full text of this article at NEJM.org). We randomly sampled an additional barrio from each of the two inhabited island municipalities off the northeast coast, Vieques and Culebra, and excluded largely uninhabited barrios such as nature reserves. 
 
 We randomly selected 35 households from each barrio using OpenStreetMap (OSM) layers to identify buildings.25 When data collectors encountered an abandoned home or nonhome structure, they sampled a house from all surrounding visible houses using a random number generator. The same process was followed if consent was declined, if the house was empty at the time of the interview, or when sparsely populated barrios had fewer than 35 points sampled because of incomplete data structures on OSM. Our survey logistics did not allow for the data collectors to revisit an empty house (see the Supplementary Appendix for details). 
 
 Data collectors did not record any personal identifiers; global positioning system (GPS) coordinates were aggregated after data collection. To avoid coercion and reduce bias, no compensation was provided. The participants were informed that their responses would not result in direct benefits to them or their families. If respondents requested health services, data collectors provided information on accessible resources identified by local partners. Consent for participation was acquired before administration of the survey. This study was granted a human subjects research exemption (45CFR46) by the institutional review board of the Harvard T.H. Chan School of Public Health. 
 
 Household Survey 
 
 We used a hybrid census method, collecting information about each household member, including all persons who had moved in, moved out, been born, or died in 2017.26 Persons who were reported to be missing from households, but not known to be deceased, were considered to be alive for our calculations. Households were defined as a person or a group of persons, related or unrelated, who live together. The survey was administered to one adult respondent per household and took less than 10 minutes to complete. The survey instrument is provided in the Supplementary Appendix. The survey included questions on age, sex, cause of death if after the hurricane, hurricane-related migration, neighborhood deaths, and access to electricity, water, and cellular network coverage on an ordinal scale for each month (0 days, 1 to 7 days, 8 to 14, 15 to 30 days, or all month). 
 
 Population Estimation 
 
 Survey weights (w) were constructed by calculating the inverse probability of selection of a household and were defined as 
 
 and 
 
 We used the following formulas to calculate the general population estimate: 
 
 and 
 
 where i is the household. Weights and estimates of excess deaths were constructed with the use of the most recent official population estimate in 2016.27 
 
 Statistical Analysis 
 
 To estimate excess deaths, we estimated the mortality rate after the hurricane (from September 20 through December 31, 2017) and compared it with the official mortality rate for the same period in 2016, since mortality rates showed seasonal but stable trends from 2010 through 2016 (Fig. S2 in the Supplementary Appendix). Official monthly mortality data for 2016 were obtained from the Department of Health 2016 mortality data provided by the Institute of Statistics of Puerto Rico.28 We computed our rate without applying survey weights, since we observed no remoteness category–specific clustering of deaths (see the Supplementary Appendix for further discussion). The post-hurricane unweighted crude mortality rate (R after ), estimated from our survey, was therefore defined as 
 
 where 102 is the number of days between September 20 and December 31, and R before is the unweighted crude mortality rate in 2017 before September 20. The standard error for R after was estimated from our survey: 
 
 We assumed deaths were Poisson distributed, and we calculated the corresponding 95% confidence interval assuming the rate would be large enough that we could assume the normal approximation for the Poisson distribution: ||||| Study Puts Puerto Rico Death Toll From Hurricane Maria Near 5,000 
 
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 Updated 12:43 p.m. ET 
 
 Perhaps 5,000 people died in Puerto Rico in 2017 for reasons related to September's Hurricane Maria, according to a study that dismisses the official death toll of 64 as "a substantial underestimate." 
 
 A research team led by scientists at the Harvard T.H. Chan School of Public Health didn't simply attempt to count dead bodies in the wake of the powerful storm. Instead, they surveyed randomly chosen households and asked the occupants about their experiences. 
 
 From that approach, they concluded that between Sept. 20 and Dec. 31, 2017, there were 4,645 "excess deaths" — that is, deaths that would not have occurred if the island hadn't been plunged into a prolonged disaster following the devastating storm. 
 
 But the estimate isn't as precise as the figure implies.The researchers calculate a statistical term called a 95 percent confidence interval, which encompasses a broad range – from 800 to 8,500 deaths. Their figure of 4,645 lies near the middle of that range, and they round up to something over 5,000 to account for some assumptions they made. 
 
 The findings were published Tuesday by The New England Journal of Medicine. 
 
 The research team randomly selected 3,299 households in Puerto Rico. Local scientists surveyed them over the course of three weeks in January. People in those homes reported a total of 38 deaths. The scientists then extrapolated that finding to the island's total population of 3.4 million people to estimate the number of deaths. The researchers then subtracted deaths recorded during that same period in 2016 and concluded that the mortality rate in Puerto Rico had jumped 62 percent in the three months following the storm. 
 
 The death rate is a contentious subject, in part because federal and island governments haven't responded as rapidly to the disaster as they have in other hurricane emergencies. The study notes that 83 percent of the households in Puerto Rico were without electrical power for the time period looked at, more than 100 days, from the date of the hurricane until the end of 2017. 
 
 Puerto Rico residents and outside observers have long argued that the official death toll is hopelessly inadequate. It captures the number of deaths the medical examiner attributed directly to the storm — the high water and howling winds in the worst natural disaster on record for the U.S. territory. Maria came ashore as a Category 4 hurricane, with winds gusting at over 110 mph and drenching rainfall. 
 
 CNN surveyed funeral homes after the storm and tallied 499 hurricane-related deaths. The New York Times compared official death records from September and October 2017 and identified more than 1,000 excess deaths, compared with the average for 2015 and 2016. Alexis Santos, a researcher at Penn State University, and a colleague, used death certificates to come up with a similar estimate. 
 
 The government of Puerto Rico commissioned researchers from George Washington University's Milken Institute School of Public Health to estimate excess deaths. Results of that study have been delayed and are due out this summer. "We have always expected the number to be higher than what was previously reported," said Carlos Mercader, executive director of the Puerto Rico Federal Affairs Administration. He says that's why it commissioned the study from GW. "Both studies will help us better prepare for future natural disasters and prevent lives from being lost." 
 
 Caroline Buckee, a lead author of the news and epidemiologist at the Harvard T.H. Chan School of Public Health, says, "Our approach is complementary to that and it provides a different kind of estimate and a different kind of insight into the impact of the hurricane." The researchers suggested that the government in Puerto Rico could use its methods in an even larger survey to reduce the large uncertainties in their findings. 
 
 The Harvard study covers a greater time period than The New York Times' calculation, a difference that could partly account for the much higher figure. 
 
 The household survey is a widely accepted technique for estimating casualties following a disaster. But it can be misleading if the sample isn't truly random or if some households have been wiped out altogether and are therefore missing from the survey. In the latter, the result would underestimate the true toll. In fact, the Harvard team says its results are "likely to be an underestimate" because of this bias. 
 
 National Communication Issues In Puerto Rico Make It Hard To Register Deaths Communication Issues In Puerto Rico Make It Hard To Register Deaths Listen · 4:04 4:04 
 
 The survey looked at deaths through the end of 2017, but the scientists suspect that the excess deaths continued into this year. "We saw consistent, high rates, in September, October, November, December," says Rafael Irizarry, a biostatistician on the research team. "There's no reason to think that on Jan. 1 this trend stops." 
 
 "Hurricane Maria caused massive infrastructural damage to Puerto Rico," the Harvard team writes in its study. 
 
 "In our survey, interruption of medical care was the primary cause of sustained high mortality rates in the months following the hurricane," the wrote. Hospitals and doctors struggled to provide care, and many people simply had trouble getting to the doctor or the hospital to seek medical care. The survey finds that one-third of the total deaths in the months following the storm were caused by delayed or interrupted health care. 
 
 Understanding the true number is important for many reasons. "There are ramifications not only for families, not only for closure, but also financial ramifications" such as for aid and preparedness, says Dr. Satchit Balsari, one of the lead investigators, who is a physician at the Harvard FXB Center for Health and Human Rights.
– The official government death toll in Puerto Rico from devastating Hurricane Maria stands at 64. A new assessment led by Harvard researchers puts the figure closer to 5,000, reports NPR. More specifically, the researchers calculate that Puerto Rico had 4,645 "excess deaths" between Sept. 20, 2017, and Dec. 31, they write in the New England Journal of Medicine. How they got the figure: Researchers surveyed 3,299 homes in January and February and turned up 38 deaths in the time period after the hurricane, then extrapolated the figure to the island's population of 3.4 million. They concluded with a 95% certainty that the death toll attributable to the hurricane is between 800 and 8,500, with the figure of 4,645 a likely estimate. They also found that when comparing the number of deaths to 2016, the island's mortality rate increased 62% in the three months following the storm. "Our results indicate that the official death count of 64 is a substantial underestimate of the true burden of mortality after Hurricane Maria," the authors write. The toll of 64 mostly counts people killed directly by rising water or wind, and the Washington Post provides an example of a death that went uncounted. Ivette Leon, 54, died at home in November, less than a day after being released from the hospital. As her condition deteriorated, it took family members 20 minutes to get cell reception to summon help, and then nonworking traffic lights delayed the arrival of an ambulance. The new study suggests there are thousands more like her. "That is an astonishing undercount," a Columbia professor who wasn't involved with the study tells BuzzFeed News. "Something has gone terribly wrong here if they have a 70-times-higher death rate."