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In mid-April, when the CDC began releasing forecast models of COVID-19 deaths, the number of official deaths was just over 22,000 and there were hopes expressed by the government that strict social distancing might limit that number to around 60,000 by mid-May (see graphic below).
That hope lay in the `low range' of the forecasts, of course - and over the last 20 days we've seen the number of deaths in the United States triple - blowing past the 60K estimate to over 67,000 today. Revised estimates now put that May 15th number somewhere between 70K and 90K.
Welcome to the useful - but not necessarily correct - world of computer modeling.Anyone who has watched the shifting forecast tracks of hurricanes - which can change with every model run - knows that even with the power of supercomputers, forecasting is an inexact science. As George E. P. Box (18 October 1919 – 28 March 2013) - Professor Emeritus of Statistics at the University of Wisconsin - famously said : “All models are wrong, but some models are useful.”
And while we can't take COVID-19 forecasts literally, they can tell us - in close to real time - what the trends are, and when and where adjustments can and should be made to change the course of the epidemic. .The CDC has updated - both the number and the format - of their forecast models as of May 1st, with the latest runs carrying out to the end of May. The addition of the ensemble model, which weighs and averages the other runs, is a welcome addition.
COVID-19 Forecasts
Updated May 1, 2020
Why Forecasting COVID-19 Deaths in the US is Critical
CDC is responding to a pandemic of coronavirus disease 2019 (COVID-19) caused by a novel coronavirus, SARS-CoV-2, that is spreading from person to person. The federal government is working closely with state, tribal, local, and territorial health departments, and other public health partners, to respond to this situation. Forecasts of deaths will help inform public health decision-making by projecting the likely impact in coming weeks.
What the Forecasts Aim to Predict
Forecasts based on the use of statistical or mathematical models (subsequently referred to as “models”) aim to predict changes in national- and state-level cumulative reported COVID-19 deaths for the next four weeks. Forecasting teams predict numbers of deaths using different types of data (e.g., COVID-19 data, demographic data, mobility data), methods (see below), and estimates for the impacts of interventions (e.g. social distancing, use of face coverings).
Interpretation of Forecasts
- This week’s forecasts include national- and state-level forecasts from additional modeling groups and “ensemble” forecasts that summarize the information from the individual forecasts.
- National-level forecasts continue to indicate that deaths are likely to rise in the coming weeks. How quickly they will increase remains uncertain and is dependent on forecast assumptions about the strength and coverage of social distancing behaviors that continue over this period.
- State-level ensemble forecasts (only shown for states and territories with at least two forecasts) indicate a slowed growth in new deaths for most states.
National Forecast
- These forecasts show cumulative reported COVID-19 deaths since February and forecasted deaths for the next four weeks in the United States.
- The CU models make various assumptions about the effectiveness of current interventions. All other models assume that existing social distancing measures will continue through the time period shown.
State Forecasts
State level forecasts show observed and forecasted state level cumulative COVID-19 deaths in the US.
Forecasts fall into one of three categories
- The LANL and UMass-MB models do not explicitly model the effects of individual social distancing measures but assume that implemented interventions will continue, resulting in decreased growth.
- The Geneva, MIT, MOBS, UT, and YYG models are conditional on existing social distancing measures continuing through the projected time period.
- The CU models make different assumptions about the effectiveness of current social distancing interventions.
Download state forecasts pdf icon[PDF – 186 KB]Download model data excel icon[XLS – 396 KB]
Working to Bring Together Forecasts for COVID-19 Deaths in the US
CDC works with partners to bring together weekly forecasts for COVID-19 deaths in one place. These forecasts have been developed independently and shared publicly. It is important to bring these forecasts together to help understand how they compare with each other and how much uncertainty there is about what may happen in the upcoming four weeks.(Continue . . . )
As always, these models are based on assumptions, including the public maintaining various levels of social distancing. If public actions deviate from these assumptions, the models will become less accurate.
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