Minnesota Governor Tim Walz promulgated his first shutdown order on March 17 before broadening and extending it a week later. The governor promulgated his current shutdown order on the basis of a model that projected in excess of 74,000 deaths due to the Wuhan virus. We have questioned the projection and asked what model it is based on.
Today the Star Tribune finally gets around to taking a look — an extremely clouded look — at Walz’s in Jeremy Olson’s story “Disease data modeling, in Minnesota and elsewhere, varies greatly.” Subhead: “Modeling by the Minnesota Department of Health and the University of Minnesota directly informed Gov. Tim Walz and guided his stay-at-home order.”
What is Walz’s model? How many lives will the current, extremely destructive shutdown save, if any? Let us extract the references to Walz’s model:
Modeling by the Minnesota Department of Health and the University of Minnesota persuaded Gov. Tim Walz to announce the current stay-at-home order. The modeling is conservative, perhaps pessimistic, about the course of the outbreak, said Stefan Gildemeister, state health economist, but the Washington model may be optimistic and overlooking risk factors in the United States that could make the outbreak worse.
“Saying that the Washington approach is optimistic is not saying that we think we’re right,” he said. “Some of our assumptions might have turned out to be unusually conservative. In fact, we’ve been saying this from the beginning. We will continue to test our assumptions and change them.”
The Minnesota modeling wasn’t designed to forecast deaths but rather how much they would decline under social distancing restrictions. Gildemeister and colleagues concluded that deaths could decline by one-third under the current stay-at-home strategy — primarily by delaying the surge of cases so that hospitals have more time to prepare.
When it comes to the death numbers, any change in assumptions makes a dramatic difference. The Minnesota researchers used hospitalization and death rates that increase with age and were first used by colleagues at Imperial College.
We have adverted several times to the Imperial College model and related problems. Olson alludes to none of this.
The local researchers also used a so-called R-naught estimate that one Minnesotan carrying the coronavirus would spread it on average to 2.5 people, whereas initial global estimates were only 2.2.
In the world of R-naughts, tenths can make a substantial difference in estimating how rapidly a virus can spread, said Dr. Frank Rhame, a virologist for Allina Health. “Over a couple of months, 2.2 and 2.5 is a big difference.”
With no interventions at all, the Minnesota model estimated 74,000 deaths in the state. Under the current stay-at-home strategy, it estimated around 50,000. However, Rhame said the reduced face-to-face contact in Minnesota could be reducing the R-naught, which in turn would reduce infections and deaths.
The addition of ventilators could help as well, as the Minnesota model predicts local hospitals will run out before the COVID-19 outbreak peaks. Globally, only around 5% of COVID-19 cases have needed hospital intensive care, and fewer yet have needed ventilators to compensate for the severe respiratory symptoms that can occur. But death risks increase dramatically when people don’t have ventilators available when needed.
The Minnesota model also assumed that people with COVID-19 needing intensive care would remain in hospital ICU units on average for 23 days. The actual length of stay could be shorter, which would mean more availability of beds and ventilators.
The length of stay “affects available resources, and that affects the timing of when we reach overcapacity, and that affects [the rate of] mortality,” Gildemeister said.
When it comes to saving some 24,00 lives at the costs imposed by the current shutdown, does anyone sense that we are walking in a wonderland of bovine excrement? Analyze this:
The Washington model suggests an improving situation in Minnesota. It predicted a death toll of more than 2,000 in the state a week ago but only 932 as of Wednesday because of the apparent impact of Walz’s stay-at-home order.
But then there is this:
One concern about the Washington model is that it doesn’t directly account for the high level of obesity and chronic disease in the U.S., which could result in more severe illnesses and deaths than in China or other countries, Gildemeister said.
The Minnesota model was based on prior studies that demonstrated that people with chronic diseases were 7.6 times more likely to die from a COVID-19 illness than people without those conditions.
Minnesota modeling has predicted only a delayed peak in COVID-19 cases and hospitalizations because of the mitigation strategies, and not a reduction of cases, but updated analysis may show differently, Gildemeister said.
Does anyone seriously believe that we will save 24,000 lives in Minnesota by preserving the availability of health care resources that would otherwise be lacking? I doubt it, but Olson lets the question escape unasked.
The question of costs versus benefits is beyond Olson, or beyond the scope of his story. Reading Olson’s story closely, however, and taking it solely on its own terms, I assess that we are at substantial risk of inflicting enormous damage on the Minnesota economy with literally no benefit in lives saved.
I’m not saying this is the case. I don’t know. I’m saying it is a reasonable inference from Olson’s story.
NOTE: See also Kevin Roche’s Healthy Skeptic post “Be Extremely Cautious About Anything You See Based on a Model.”