In the field of online research, and particularly with respect to online access panels, the amount of information the research institute should provide its respondents with when sending out invitations is still discussed quite controversially.

On the one hand, revealing too many details holds the risk of self-selection among potential participants. Furthermore, if the topic is explained, experienced panellists only interested in incentives might adjust their answers to the screening questions in order to take part in every possible survey. Such behaviour is likely to cause untrue statements and bias in the studies’ results.

On the other hand, not including enough information in invitations involves the risk of potential participants deciding not to take part in a survey as they are, for instance, unsure about the incentives or the amount of time they have to invest in order to complete the questionnaire.

Consequently, the following questions arise:

Is it sufficient to just inform the panel members that there is a questionnaire waiting for completion? Should information on the length of the survey, the field time and the incentives paid for completion be included in the email? Or would it even benefit the response and results to announce the topic of the survey?

The lecture aims at eliciting answers to these questions.

It is based on an empirical study including about 30 experiments with 1000 respondents each. In the course of this study, the invitation-emails were systematically varied, and the different response rates were monitored.

The information content of the emails was differentiated in a way that one part of the panellists always received a mail containing extensive information about the study, whilst two additional groups either received information regarding the questionnaire’s length and the incentive or were informed about the topic of the survey. A last group finally obtained an invitation only including a link to the questionnaire but no additional information describing the survey at all.

The analysis of the projects realised aims at identifying and presenting the optimal information content of email- invitations for online surveys.