Last December, a week before the holiday break, I received a call from the government of Puerto Rico seeking a meeting to discuss Hurricane Maria and its aftermath. In the cab on the way to meet Gov. Ricardo Rosselló, I knew the number of Puerto Rican lives lost was, and would continue to be, a highly charged issue. But I had no idea that after the Milken Institute School of Public Health, of which I am the dean, released our independent study, that the issue would be the subject of several presidential tweets.

The tweets suggested a political motive for our study’s finding of 2,975 excess deaths in Puerto Rico after Hurricane Maria.

To set the record straight, our study was carried out with no interference whatsoever from any political party or institution. It was based on a careful examination of all of the deaths officially reported to the government of Puerto Rico between September 2017 and February 2018. Our scientists, in collaboration with scientists at the University of Puerto Rico Graduate School of Public Health, used state-of-the-art mathematical modeling to compare the total number of deaths during that time to the expected number of deaths, based on historical patterns as well as age, sex, socioeconomic status and migration from the island.

Make no mistake: The death toll did continue to rise in the months after Maria. In September 2017, when Puerto Rico recorded a total of 2,906 deaths, we found there was an excess of 574 deaths above what would have been expected in a year without the storm. The death toll continued to mount every day, with an excess of 697 deaths in October, 347 in November, 479 in December, 558 in January, and 320 in February, for a total of 2,975.

Throughout that time, researchers produced other estimates. The government of Puerto Rico came up with a figure of 64 excess deaths through October 2017; The New York Times, 1,052 through October 2017; a team at Harvard University, 4,645 through December 2017; and researchers at Penn State University, 1,139 through December.

Of these, only the estimate by the government of Puerto Rico involved the examination of individual deaths to determine if the hurricane had caused them. The Harvard study, based on a household survey, was later found (by Milken Institute School of Public Health researchers) to have overestimated the number of deaths because it did not adjust the household death reports for household size. When analyzed correctly, their study produces similar numbers. The other two studies, like ours, used death certificates.

Ours was the only study that took into account the enormous net out-migration of citizens that occurred after the storm. According to our estimates, in mid-September 2017 there were 3,327,917 inhabitants in Puerto Rico; by the end of February 2018 there were only 3,048,173, a net loss of about 8 percent of the population. This is the main reason why our analysis produced somewhat larger estimates than the other studies.

We do not know the exact circumstances surrounding each of the 2,975 excess deaths that occurred. Many factors – disruption in transportation, access to food, water, medications, power and other essentials – may have contributed. In interviews, we heard many heartbreaking stories of families struggling to obtain emergency health care, power for medical devices, prescription drugs, or even food and drinking water. This is why we were not surprised to find that the highest rates of excess deaths occurred among those living in the poorest municipalities, as well as those over the age of 65, especially men.

The federal government and charities have provided tremendous resources to Puerto Rico, and we are proud of the hard work of the local citizens and leaders, federal responders and volunteers who risked their own lives to pitch in and help. What was lacking was adequate planning and preparedness for such a horrific storm. No one administration or political party is responsible for why we still don’t prioritize preparedness even though we are increasingly threatened by large hurricanes. By identifying the preventable causes of these deaths, we can save lives the next time a fierce storm hits.