One thing to note about serological studies is that as enrollment is voluntary you are likely to over select the "potentially" Covid-infected (as they would be more curious about assessing antibodies in their system). This would also partly explain the order of magnitude difference between serological data and administrative data on Covid infections.,(reply>), @Sarah Fox How?,(reply>), @Sarah Fox I did not see the studies. How did they adjust for this type of self-selection (I assume they did not estimate Heckman selection models)?,(reply>), They adjust for that