Wednesday, July 15, 2020
There have been recent media reports about positive testing rates increasing in Pennsylvania. I thought I would take a closer look at positive test rates since they were reported by the state on April 17. The positive testing rate is simply the number of positive tests divided by the total number of tests. The graph above shows the cumulative positive test rates for the US (orange line), PA (red line), and Cambria County (blue dotted line). The black line shows the daily positive testing rate for Cambria County.
The positive rate for the state has been consistently higher than the US and county rates. Both rates have been decreasing as testing has become more readily available. Cambria's positivity rate has been consistently lower than the state and US rates. The daily testing rate for the county on April 13 was high because on that day there were three positive tests out of 16 total tests (18.25%).
Since June 24, the cumulative positive test rate increased from 1.02% to 1.28% as of today. This rise may not sound like much but the solid black line shows positive rates that were consistently at or above the cumulative rates for this period with one day being higher than 5% on July 11.
The graph above is from the Johns-Hopkins Univeristy site tracking the Corona Virus Pandemic. It shows the trend in testing for the US during the pandemic. The blue line shows the seven day average of positive test % with a steady decrease from early April (21.9%) until the middle of June (4.4%) with an increase to 8.7% today.
This graph shows the trend in testing for the state of Pennsylvania for the same period. Here, we see that there was a corresponding peak in mid April in the positive rate at 27.8% to 3.4% around June 21. This decrease was followed by an increase to 5.5% as of today. We can see that testing has risen at a slower rate in the state than in the US as a whole.
The black line in the graph at the top was replaced with the 7 day moving average in testing which does show a rise in positive tests after June 24. I did not have the same access to
testing data that Johns-Hopkins had. I used publicly available data that the PA health department provided beginning on April 17.
The graph below shows the comparison of the positive testing rate (in the red line) to the testing rate as a percentage of the population for six Johnstown zip codes, the overall rates for Greater Johnstown, Cambria County, Pennsylvania, and the US. These rates are cumulative. The numbers at the top of each bar are the cumulative testing rates as a percentage of the population. It's interesting that the state has a higher cumulative positive rate (10.08%) than its testing rate (7.57%). Johns-Hopkins testing tracker has the state ranked 47th in the testing rates over the last two weeks (1.1 per 1,000) while it ranks 37th in the two week average positive testing rate (5.5%). At the bottom is a summary of testing data for Pennsylvania. How one frames the statistics makes all the difference.