Covid-19 Update: May 5, 2020

Positive rate stable as testing increases… Rural-urban divide…

One of the metrics of how well the pandemic is being tracked is whether the percent of people testing positive goes down over time. In other words, are we testing more people not exposed to the disease so we can know where it is and isn’t. The data for this are not particularly good; covidtracking.com has collated them together from each state website. Some states do no not report tests by private labs, some do. With that large caveat, I plotted all of the testing reports from all states and territories with more than 100 cases. The median values have been stable at around 9% for weeks. The upper outliers are coming down, which were NY and NJ, as those two states appear to be getting ahead of the cases. [All of the outliers from the box plots are shown as circles]. The next chart shows the nationwide growth in testing relative to cases. The rate of testing does seem to be accelerating relative to cases. Rhode Island has tested more as percentage of population than any other state.

State-reported positive rates for covid-19 tests as compiled by covidtracking.com. Blue line traces median value, which has remained stable at 9% for weeks. Outliers (NY, NJ) are included and are declining as testing gets ahead of disease spread.

Total tests administered and positive results (top) and all state testing reports with spline fitted. Rhode Island and New York have the highest state-level testing efforts on a per capita basis thus far. Data from covidtracking.com and rely on inconsistent state-level reporting.

The urban-rural patterns continue, with the most cases per capita in the most densely populated states. That number appears to be starting to level off, driven by numbers from NY. The interesting thing in looking at cases by population density is that the third quintile of density has higher levels of covid-19 than the second. That third quintile (95–177 people per square mile) includes Michigan and Louisiana, which are influenced by their large cities and, of course the decision to hold Mardi Gras in the case of Louisiana. The second quintile of density contains California, Florida, Georgia, and the most recent data show it trending up.

Average of state death rates from covid-19 over time, organized by quintiles of population density. Data from covidtracking.com at U.S. census.

As I map the death rates for the states, the northeastern focus of the outbreak is clear, with New York closing in on 0.1% of the population having died. Louisiana, Michigan, and Illinois join the northeastern seaboard with high rates. More nuance about the lower death rates is shown in the last map, which puts the color ramp on a log scale. The every low death rates in Montana and Wyoming are apparent and the eagerness of those states to reduce (or never start) restrictions on movement is understandable in that context.

State-level death rates from Covid-19 as of May 5, 2020. Color ramp is linear. Data from covidtracking.com.

State-level death rates from Covid-19 as of May 5, 2020. Color ramp is logarithmic. Data from covidtracking.com.

As students in my old Numbers and Maps course would know, these last two maps are also an example of how color scheme can be used to tell different stories with the same data. Neither of them is more “right” than the other and both of them are “wrong” in the sense that the whole state is filled in with the same color when cases are concentrated in particular areas. One shows us the “two Americas” of the pandemic so far, the other lets us compare the states with lower death rates more easily.