E-mail is a common invitation mode for Web surveys. However there are limitations in conducting Web surveys of the general population because lists of all Internet users and their email
addresses do not exist. So it is impossible to select a random sample of e-mail addresses (compared to RDD for the telephone). One solution could be to collect e-mail addresses in another mode (e.g. via CAPI or CATI interviews). But asking for e-mail addresses may raise privacy concerns among respondents. We test whether an invitation by a mailed letter could be an alternative to the common e-mail invitation in a Web survey. In this experiment participants were recruited with the aid of the German General Social Survey (ALLBUS), a face-to-face survey using computer assisted personal interviews (CAPI) in private households, conducted in 2012. Among ALLBUS respondents who reported having Internet access at home, we asked a random third for their e-mail address: 43% provided their e-mail address, while 57% declined to do so. As a control group two thirds of the Internet users were not asked for their e-mail address. In a follow-up Web survey, to be conducted in February 2013, the three groups of Internet users (those who provided an e-mail address, those who were asked but refused to provide an e-mail address, and those not asked for an e-mail address) will be invited to a Web survey by a mailed letter. We will examine the response rates to the Web survey among the three groups, and explore potential demographic and attitudinal differences of respondents, based on ALLBUS data. Our expectation is that those who provided an e-mail address will be the most cooperative, while those who were asked but refused will be least likely to respond to the Web survey.