I think you'd call individuals(using a method with far less self selection bias) and get them to fill out the same questionnaire and then do the same types of a

I think you'd call individuals(using a method with far less self selection bias) and get them to fill out the same questionnaire and then do the same types of adjustments you'd do with race or gender. But I also agree they 100% did not do any of these adjustments if they did it would be listed right here > We report the prevalence of antibodies to SARS-CoV-2 in a sample of 3,330 people, adjusting for zip code, sex, and race/ethnicity. We also adjust for test performance characteristics using 3 different estimates: (i) the test manufacturer's data, (ii) a sample of 37 positive and 30 negative controls tested at Stanford, and (iii) a combination of both.