COVID-19 Test Statistics

Nearly all the statistics we're shown about COVID-19 online and in the media are very misleading because we're only seeing the total number of people with positive test results. This information by itself doesn't tell us anything, for example, imagine you're told that country X with a population of 20 million only has only 5 positives - that sounds like great news. That's the kind of contextless information we're getting, you can see the problem clearly if I then tell you that country X has only performed tests on 10 people! That drastically changes the picture, because the information has been put into context. We're told that we need to be flattening the curve because the confirmed cases are going up so fast, but the reality is that its almost always just the number of tests that's going up. When the confirmed positives are shown as a pecentage of the total tests done, the picture is often very different - the percentage for most countries over the last month is actually flat or declining.

There's a Wikipedia page called COVID-19 testing which maintains the total numbers of tests taken and positive results for each country, using the data from the available official sources for those countries. I've put together this simple site which collects the data from the Wikipedia page each day and displays it on the chart below so you can see clearly how the data has changed over the last month or so. You can see the code here.

The red line is the confirmed positives for the selected country, which is the only data we're really seeing anywhere (along with the number of deaths). The blue line (which you can turn on and off with the checkbox) is the total number of tests taken in the selected country. Finally the green line is the most imformative information that we should be seeing everywhere - the percentage of the confirmed positves from the total tests taken.

Note that even though knowing the percentage is better, it still doesn't give us the situation in great detail, because we don't know in the case of each country the nature of the testing. Many countries only have the resource to test people after they are in a serious condition and have gone to hospital, so a very high percentage of people will test positive compared to countries like Germany where many tests are performed on people with only mild or even non-existent symptoms. To get a really clear understanding of the situation, we need more tests on completely random samples of the country's populations. For further reading, here's a good page I found highlighting some thought-provoking facts on the subject.

  % Positive
Country: Show total tests:
  Total number of tests done
  Number of confirmed positives