Most general population surveys have suffered from heavy self-selection bias or insufficient specitivity. In the early days, yes, the Bay Area was probably mis

Most general population surveys have suffered from heavy self-selection bias or insufficient specitivity. In the early days, yes, the Bay Area was probably missing 90% of cases. Testing has ramped up though (it's pretty easy to get a test if your symptomatic), so I don't believe we're missing 90% of symptomatic cases [as defined by this survey] at this point (which is part of the reason that new cases/day have remained stable while hospitalization numbers are dropping). Think about it: if people take a survey that says they have covid symptoms, wouldn't they get tested?