6. Spectrum bias
When a diagnostic test is studied in one setting – for example, in hospitals – and not in the intended population for which it is used – the community – problems with interpreting the results occur. Mass testing has taken off and the limitations of widely-used tests such as PCR have been ignored.
PCR tests on their own cannot distinguish whether you are actively infected and infectious or whether you are recovering from the disease and simply have dead particles of Covid in your system. Up to a year ago a handful of laboratories were doing PCR – a highly delicate and specialised technique, vulnerable to contamination. The enormous expansion of testing in the community has meant procedures and training have been rushed through.
Warnings by bodies such as the College of American Pathologists of the problems of using different uncalibrated PCR kits have been ignored.
The detection of ‘cases’ in the community tell us little (apart from driving lockdowns). How many are serious; how many are contagious? No one knows.
Prof Carl Heneghan & Tom Jefferson
https://www.spectator.co.uk/article/...ovid-19-biases