Using experts' consensus (the Delphi method) to evaluate weighting techniques in web surveys not based on probability schemes

Weighting techniques in web surveys based on no probability schemes are devised to correct biases due to self-selection, undercoverage, and nonresponse. In an interactive panel, 38 survey experts addressed weighting techniques and auxiliary variables in web surveys. Most of them corrected all biases jointly and applied calibration and propensity score adjustments. Although they claimed that sociodemographic and web-related variables are the most useful auxiliary variables to employ in adjustments, they considered only sociodemographic variables to correct biases because of their availability.