Schonlau, Matthias, Arthur van Soest, and Arie Kapteyn. “Are `Webographic’ or Attitudinal Questions Useful for Adjusting Estimates from Web Surveys Using Propensity Scoring?”. Survey Research Methods 1, no. 3 (December 31, 2007): 155–163. Accessed July 13, 2024. https://ojs.ub.uni-konstanz.de/srm/article/view/70.