Is the Increase in Cases Just an Artefact of Increased Testing?
by Dr Clare Craig FRCPath The story of how false positive test results can create the illusion of actual infections in the population will be a familiar one by now for many readers of this site. Assuming that the false positive percentage remains reasonably constant, then increasing numbers of tests inevitably lead to a higher absolute number of false positive test results over time. Uncritical policy decisions made without discounting for this effect have no evidenced-based validity. One real potential problem as the number of tests increases, however, is that the underlying number of actual cases – and their location – may ironically be somewhat obscured by steadily increasing and randomly distributed false positive results, caused by the higher volume of testing. By contrast, a rapid rise in the percentage of tests that are returning positive results should normally indicate that the real number of Covid cases is increasing and the false positive results will become less and less important because they are usually constant. Unfortunately, the acceleration we have seen in the recent case numbers is increasingly out of synch with crucial data from other sources. The ONS random population sampling, Zoe App and NHS triage data all show a slowing and even a plateau in the number of actual cases in the last fortnight. Either the data in all ...
