Hopeful Trends in COVID-19 Growth Rates

Some US states, like California, have declining growth rates in COVID19 cases, others, like Massachusetts, are in trouble.

This chart shows, per state and for the US, the trend in the growth rates of COVID19 cases.

Each day, the number of cases is increasing, but by a smaller percentage each day. If today had 30% more cases (for instance) than yesterday, tomorrow may have only 28% more than today. That decrease means the growth will eventually be zero, then then we will have no more cases.

The X axis is days since the state had 100 cases, and the points are the growth rate over the previous day. The line is the trend of the points. The light blue region is the 95% confidence band. A more narrow band indicates the data is closer to the trend line, and the predictions of the trend are better. Very wide bands, such as for Michigan, mean a high uncertainty in the prediction.

Over all, this chart should inspire hope. Most of the states are on a good trend, with the rate declining over time. New York is bad, but the last three days are a good trend. Massachusetts looks really bad — its trend is up, and it has a narrow band. The other states that are increasing have high error bands, and the most recent trend is down, so they may actually be moving in the right direction.

For states with a strong downward trend, like California, the predicted day number when the growth rate is zero is about day 30, which for California is in about two weeks.

This data is from Johns Hopkins, process by the Data Library, and published here.