In recent years, online questionnaires have established themselves as an indispensable part of the data collection toolkit. Respondents for the surveys are chiefly recruited from online access panels. However, surveys carried out using online access panels are limited on account of internet access times and the identity of panel members. Members in online access panels can only take part in questionnaires if they are online on their PCs and if they check their emails regularly and can identify the invitation email amongst the host of spam emails. As field times become ever shorter, certain groups of people are being excluded more and more often from taking part in these kinds of surveys. The use of mobile invitation and survey methods opens up new opportunities and leads to an improved sample quality. On the basis of several field experiments, these opportunities were examined and verified in terms of the following two hypotheses:

H1: Sending reminder invitations in the form of mobile text messages gets a higher and more rapid response rate than reminders sent per email.

H2: Carrying out mixed-mode online interviews via mobile and PC-based access routes leads to a more accurate reflection of the gross sample.

The unique nature of the identity of members in online access panels is a crucial condition for the accuracy of the survey results. In registration processes to date, the uniqueness of identity has been established first and foremost by checking the participant's email address. Clearly such addresses are not unique and can be assigned any number of times. The use of mobile channels in this case opens up new opportunities. Using a specially developed mobile verification system, access to online questionnaires is only possible following a mobile double opt-in process. The unique identity of future participants is established by requesting the participant's mobile telephone number. Multiple participation and multiple registrations in the online panel are thus made considerably more difficult. This process means that standardized double memberships can be avoided. The outcome of the comparative study will give an insight into the extent to which it is possible to achieve a better quality of data by using Internet-enabled mobile devices and whether this really does have a positive effect on the quality of the results.