We have been recently inundated with statistics about COVD-19. There is a wealth of information being accumulated by the Johns Hopkins Coronavirus Resource Center, the New York Times, the Washington Post and others. There are data by state, county and city. This post attempts to make some sense out of all this information.

Totals versus totals per population

If you watch any television news show lately theres is a box in the upper right hand corner that displays total cases in the world, total deaths in the world, and then the same data for the United States. These raw numbers are impressive and it is important to look at the total picture in this way, but there are some real limitations.

For one thing, these numbers mix up what has happened in the past with what is happening now. Another limitation is that there is not just one epidemic in the world and in the U.S., but many localized epidemics that all have different curves. If we see that the curve is “flattening” for the whole U.S., that obscures what may be happening as the epidemic spreads across the country.

A statistic that gives more useful information is cases and/or deaths per 100,000 people. That gives a better idea of what proportion of the population of a given country, state, county or city is affected by COVID-19.  For example, the county of Bureau, Illinois has only 12 total cases, but that translates into 36.4 cases per 100,000 people. This information is available on the Johns Hopkins Coronavirus Resource Center web page. If you click on any county on the map, a little box pops up that tells you the total cases and deaths in that county and also the cases and deaths per 100,000 people in that county. The Johns Hopkins site is not for the fainthearted, however. It is easy to get overwhelmed by the vast amount of data and the multiple ways the data are displayed. The New York Times has a map that has a tab to display data by population. This is a little more straightforward than the Johns Hopkins site. If you hover your cursor over the map, it gives you county level data by population. An easier way to look at the information is to look at the list of states below the map. If you don’t see your state there, the click the “Show All” button at the bottom and all the states will be listed. If you click on any state, the state’s statistics are listed at the top followed by data for each county within the state. The counties are ranked by decreasing numbers of cases. The New York Times coronavirus coverage is available for free without a subscription.

New Cases per Day

Looking at new cases per day gives a better idea about what is happening now with the pandemic in any given locality. Again, the New York Times has this information. If you scroll down below the map of U.S. cases, you will see graphs showing new cases per day by state, and which ones are increasing, decreasing, or staying the same. Unfortunately, these graphs are not adjusted for population.

Rate of change of new cases

This statistic gives a good idea of where the hot spots in the country are. Even if the number of cases is low, if they are increasing rapidly that is a sign that exponential spread of the virus may be happening, as discussed in my post on epidemiology. The best place to see this kind of data is the Dartmouth Atlas Project COVID-19 mapping. This map is organized by Hospital Referral Regions (HRR’s). These are larger than counties and sometimes cross county and state lines. There are 306 HRR’s in the U.S. Looking at data this way gives a much better idea of how hospital capacity will be affected by increased numbers of cases or hospitalizations within a given hospital referral region. This map is very easy to use and is reported by population. There are maps for cases, deaths, and average daily growth rate of cases. For example, the St. Cloud Minnesota HRR has the highest case growth rate in the country, increasing by 43.2 cases per day over the last week. This is more than three times as high as the next HRR, Sioux City Iowa, which is increasing by 13.7 cases per day over the last week.

The Dartmouth maps emphasize the problem with looking at data for the United States as a whole. It looks like the curve is flattening for the whole country, but the mid-west is starting to experience a major increase in cases and will probably be the next epicenter of the epidemic.

Summary

The most useful numbers for cases and deaths for any state, county, city or hospital referral region are numbers per 100,000 people rather than total numbers for any locality. Number of new cases per day and rate of change of new cases give a better idea about what is happening now for any locality. The New York Times and the Dartmouth Atlas are the most user friendly.