With respect to your article on the revolution in DIY Covid testing (Big Read, June 4) both critics and advocates of “lateral flow devices”, otherwise known as rapid antigen tests, are overlooking a simple solution to the problem of their seeming to be less accurate than the so-called “gold standard” PCR tests.
The low cost, ease of availability and quick results offered by rapid antigen tests mean that they can be repeated twice or even three times in succession for much lower cost than the PCR test.
Elementary statistics, surprisingly unappreciated, tells us that repeating a test increases its accuracy.
For example, if the chance of a false negative from a rapid antigen test is 10 per cent — which would be of concern since it may lead to a failure to isolate an infected person — independently applying the test twice, and taking the result overall as negative only if both individual test results are negative, lowers the chance of a false negative to 1 per cent. Routinely undertaking such test repetition offers an accessible approach to mass testing that combines low cost, accessibility and ease of use with high accuracy.
Sanjay G Reddy
Department of Economics,
The New School for Social Research,
New York, NY, US