Web-based surveys are increasingly perceived as a well-accepted data collection methodology. However, not enough is known about differences between people who do and who do not participate in such surveys. While there is a growing body of research on strategies for increasing response rates, little is known about their differential effects on sample composition.

Within our research project, funded by the German Research Foundation DFG, we study how selected strategies proven to be effective in increasing response rates affect sample composition in terms of values, personality traits, and civic duty orientation—variables that are frequently measured in surveys in sociology, psychology, and political science. We collected baseline data about these characteristics within the German General Social Survey (ALLBUS 2008). Subjects with Internet access were asked to participate in a Web-based survey. Of those ALLBUS respondents with Internet access (around N=1900), 42% expressed their willingness to participate (around N=800) in the follow-up survey. In this survey, we conducted an experiment with three versions of prenotification (by postal mail, e-mail, or none) and three versions of promised feedback (none, about oneself, or about other participants). The experimental study was administered between November and December 2008. We will present first results on the expected differential effects, portray avenues for future research, and will discuss the study’s implications. Specifically, the results should help researchers using Web-based surveys to recognize the combinations of strategies for increasing response rates that may encourage (or discourage) respondents with particular traits and values, and could therefore lead to biased survey estimates.