The survey’s individual response files contain respondent weights calculated by Facebook. These weights are also used to produce our public contingency tables and the geographic aggregates in the COVIDcast Epidata API.
Facebook has provided documentation to describe the calculation and usage of these weights, available here. This documentation explains the weight methodology, gives examples of how to use the weights when calculating estimates, and states the known limitations of the weights. We also have separate information about the survey’s limitations that affect what conclusions can be drawn from the survey data.