Schnell, Rainer, Marcel Noack, and Sabrina Torregroza. “Differences in General Health of Internet Users and Non-Users and Implications for the Use of Web Surveys”. Survey Research Methods 11, no. 2 (August 7, 2017): 105-123. Accessed May 17, 2022. https://ojs.ub.uni-konstanz.de/srm/article/view/6803.