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 didn't simply attempt to count dead bodies in the wake of the powerful storm. 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). 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.
– 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."