Tuesday, March 9, 2021

The Covid model that 'keeps being wrong'

This coronavirus model keeps being wrong. Why are we still listening to it? Vox - Kelsey Piper: 

May 2, 2020 - "How many people are likely to die in the United States of Covid-19? How many hospital beds is the country going to need? When will case numbers peak? To answer those questions, many hospital planners, media outlets, and government bodies — including the White House — relied heavily on one particular model out of the many that have been published in the past two months: the University of Washington’s Institute for Health Metrics and Evaluation (IHME).

"The model first estimated in late March that there’d be fewer than 161,000 deaths total in the US; in early April, it revised its projections to say the total death toll through August was projected to be 60,415 (though it acknowledged the range could be between 31,221 and 126,703). 

"The model has been cited often by the White House and has informed its policymaking. But it may have led the administration astray: The IHME has consistently forecast many fewer deaths than most other models, largely because the IHME model projects that deaths will decline rapidly after the peak — an assumption that has not been borne out.

"On Wednesday [April 29], the US death count passed the 60,000 mark that the IHME model had said was the likely total cumulative death toll. The IHME on April 29 released a new update raising its estimates for total deaths to 72,433, but that, too, looks likely to be proved an underestimate as soon as next week. Even its upper bound on deaths — now listed as 114,228 by August — is questionable, as some other models expect the US will hit that milestone by the end of May, and most project it will in June. [U.S. figures showed 110,000 deaths by June 1 - gd]

"One analysis of the IHME model found that its next-day death predictions for each state were outside its 95 percent confidence interval 70 percent of the time — meaning the actual death numbers fell outside the range it projected 70 percent of the time.... This track record has led some experts to criticize the model. 'It’s not a model that most of us in the infectious disease epidemiology field think is well suited' to making projections about Covid-19, Harvard epidemiologist Marc Lipsitch told reporters.... Yet it’s the IHME model that has generally guided policymakers, for the most part, in the direction of focusing on a return to normal....

"The criticism of the IHME model, and an emerging debate over epidemiology models more broadly, has brought to light important challenges in the fight against the coronavirus. Good planning requires good projections. Models are needed to help predict resurgences and spot a potential second wave. Dissecting what the IHME model got wrong, what other models got right, and how the public and policymakers read these models is essential work in order to create the best pandemic plans possible....

"Models usually lay out some foundational assumptions and offer projections based on those assumptions. The IHME model seeks to project death rates and hospitalization rates assuming widespread social distancing and strong measures to prevent the spread of the virus. But as the weeks have passed, it has become clear that the IHME’s projections have been too optimistic, and slow to adjust to reflect the fact that deaths have plateaued rather than rapidly decreasing to zero. The IHME has been regularly updating its model as new data comes in, but the updates have often been slow enough that the numbers are absurd by the time they’re changed in an update. For example, in late April the model still stated the expected total death toll was 60,000, even as the US was clearly only a few days from that milestone.

"[IHME researcher Ali Mokdad] Mokdad told me when we talked that a fix was in the works, and it went up a few days later: The model now projects 73,433 deaths by August. That, too, is probably an underestimate — most other models project that total will be reached next week." [U.S. figures showed over 188,000 deaths by August 30 - gd]

Read more: https://www.vox.com/future-perfect/2020/5/2/21241261/coronavirus-modeling-us-deaths-ihme-pandemic

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