Understanding how researchers are predicting spread of coronavirus

A handful of models disagree about what the timeline of the coronavirus in the U.S. could look like in the months ahead, something University of Washington biology professor Carl Bergstrom expanded on in a recent thread on Twitter.

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UW’s own model predicts that coronavirus deaths in the United States will peak around April 16, and will arrive alongside a shortage of over 36,000 hospital beds, and nearly 25,000 ventilators.

That’s also the model Bergstrom points to as a best-case scenario.

“The (University of Washington) model strikes me as a best case model (at least given current data inputs) and its confidence ranges represent uncertainty around that best case, not best-to-worst cases,” he pointed out.

The so-called “worst-case” model comes from Imperial College, which predicts between 1.1 and 1.2 million coronavirus-related deaths in the United States, “even with mitigation efforts.”

“We’ve got best-case models that predict on the order of 100,000 U.S. deaths and worst-case models that predict on the order of 1,000,000 U.S. deaths,” Bergstrom noted. “Where are the middle case models? Why aren’t we seeing those?”

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Bergstrom uses the metaphor of a rolling a boulder down a ridge line as an example of why we’re not seeing those “middle ground” models that split the difference between a best and worst-case scenario.

“Imagine rolling a ball along a ridge line,” he described. “It *might* track right down the center of the ridge the whole way, but far more likely it will end up on one side of the ridge or the other.”

7. Imagine rolling a ball along a ridgeline. It *might* track right down the center of the ridge the whole way, but far more likely it will end up on one side of the ridge or the other.

Pretty subtle differences in starting position and angle make a big difference in outcome. pic.twitter.com/7br1OXzZ1s

— Carl T. Bergstrom (@CT_Bergstrom) April 6, 2020

“Epidemics work a bit like that,” he continued. “Either you manage to suppress the epidemic and end up on one side of the ridge, or you lose control of it and end up on the other. There is some middle ground, but not much.”

Given the variance between the best and worst cases, he concludes that when enacting policies based on these models, health officials need to understand the context.

“When making policy recommendations, one has to take the scope and intent of the model into account.”

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