When Delphi-Facebook and the U.S. Census Bureau provided estimates of COVID-19 vaccine uptake last spring, their weekly reports drew on responses from as many as 250,000 people.
The data sets boasted statistically tiny margins of error, raising confidence that the numbers were correct. But when the Centers for Disease Control and Prevention reported actual vaccination rates, the two polls were off — by a lot. By the end of May, the Delphi-Facebook study had overestimated vaccine uptake by 17 percentage points — 70 percent versus 53 percent, according to the CDC — and the Census Bureau’s...
Read more about HDSR's Xiao-Li Meng on Biased Vaccine Surveys