Abstract
A method using questionnaire data for estimating the level of under
reporting during an outbreak is presented. It is based on rewriting the
conditional probabilities for getting tested, being infected, and having
symptoms. It shows very good agreement with seroprevalence studies of
blood donors. On the one hand, this shows the strength of questionnaires
when testing the general population during an outbreak as a means to
find the true prevalence. On the other, applying it to covid-19
demonstrates that the asymptomatic cases likely make up around 50% of
the infected.