An Analysis of Alabama COVID-19 Cases for May Through July
The first topic I would like to dive into is the cases reported by the Alabama Department of Health for March 13th, 2020 through July 31st, 2020. This is the earliest and latest data available as of this writing. The primary question I will be looking at is are the number of cases rising due to more testing or are cases actually going up?
Figure 1 shows the cumulative tests and cases by day as well as the rolling 14 day percent positive average. A cursory review of the graph shows that cases to broadly follow the same pattern as total tests but the increased percent positive rate indicates that testing does not fully explain the increased cases.
Figure 2 shows the rolling 14 day average for tests and cases as well as the same percent positive data as Figure 1. This graph shows that testing has increased from around 4,000 on May 1st to 10,000 in late July. Logically if tests are doubled then you will also see an increase in positive tests. But as before, the increased testing does not account for the entire increase in cases.
For my analysis I will be using data from May and July. I do not want to use April as the testing was still low enough that in my opinion the data will not be useful. As the graph shows that is when the percent positive also stabilized so I believe May and July will provide a fairer comparison than April and July.
Figure 3 shows the data I will be using for my analysis in the first two rows and the analysis itself in rows 3 and 4. The total difference in cases we are trying to investigate is 36,859.
First, you will notice tests per day in July are more than double the tests per day in May. To work out the effect of the increased testing volume I used the following equation: (July Tests-May Tests) x May Rate. That works out to a difference due to test volume of 12,045, 32.68% of the total.
To determine the effect of the increased percent positive we simply use the formula (July Rate-May Rate) x July tests. This works out to 24,814 or 67.32% of the total.
In summary, it appears case counts are actually increasing. With 67% of the increase in cases explained by more frequent positive tests it seems clear the cases are legitimately going up.
