Hurricane Maria left a trail of devastation whose effects are still being felt to this day in Puerto Rico. On Tuesday, a new study from George Washington University’s Milken Institute School of Public Health—and commissioned by the governor of Puerto Rico—concluded that there were an estimated 2,975 deaths on the island related to the storm. That’s a far bigger number than initially thought, and those affected tended to be the elderly and the poor.
But here’s something that may cause some confusion—why have the numbers on Maria’s death toll varied so widely?
Originally, a government figure pegged the death toll at 64. That simply didn’t pass the smell test for many observers—and for good reason. As my colleague (and Fortune editor in chief) Clifton Leaf explained in an excellent piece back in May, that official number only involved the number of deceased people who were specifically seen by a medical examiner. A region lacking in robust medical and transportation infrastructure in the midst of an historic storm isn’t the most amenable venue for those requirements.
In August, a new government report admitted that the figure was closer to 1,400. “Although the official death count from the Puerto Rico Department of Public Safety was initially 64, the toll appears to be much higher,” wrote the report authors. “On June 13, the Government of Puerto Rico revealed that there were 1,427 more deaths in the four months after the hurricanes than normal (based on the previous four years), and it will update the official count after a George Washington University study is completed.”
That George Washington University study is now complete and has more than doubled even the government’s revised death toll projection (another paper published in the New England Journal of Medicine earlier this summer actually goes even further and posits a death toll of 4,645.)
So what accounts for these wildly divergent numbers? To put it simply, it’s the methodology. Both the NEJM study and George Washington University paper attempt to incorporate the longer-term, and less easily measurable, potential effects of a devastating natural disaster—such as the downstream consequences for low-income residents and elderly people who didn’t have access to adequate food, water, and other resources to begin with.
“The official government estimate of 64 deaths from the hurricane is low primarily because the conventions used for causal attribution only allowed for classification of deaths attributable directly to the storm, e.g., those caused by structural collapse, flying debris, floods and drownings,” says the latest report in an attempt to explain the initial undercount. “During our broader study, we found that many physicians were not oriented in the appropriate certification protocol. This translated into an inadequate indicator for monitoring mortality in the hurricane’s aftermath.”
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