Before revision:  We simulated multiple models currently used to study the COVID-19 pandemic and computed the relation between these two fractions in all those models . Across most models currently used and for most realistic model parameters, the relation between the two fractions is consistently linear and model independent. This relation can be used to estimate the number of undiagnosed infected, with no explicit epidemiological model. We apply this method to measure the number of undiagnosed infected in Israel. Since the fraction of confirmed cases with a known source can be obtained from epidemiological investigations in any country, one can estimate the total number of infected individuals in the same country .
After revision:  We simulated multiple models currently used to study the COVID-19 pandemic and computed the relation between these two fractions in all those models . Across most models currently used in the study of epidemics, independently of the total number of infected individuals in the same country .