The effects of a special sequential mixed-mode design, and reminders, on panellists' participation in a probability-based panel study.

The sequential mixed-mode strategy has become standard practice in the survey management of longitudinal studies, in order to achieve consistently high response rates. To realise this aim in a cost-efficient way, a first mode is often an online questionnaire, towards which the target persons are pushed, and a second mode is then a telephone interview, offered to those who do not respond to the initial mode. However, the rationale for using the sequential mixed-mode plus "push-to-web" strategy to reduce the burden of choosing between survey modes, in order to maximise survey participation, could be undermined if there is an overlapping field period during which the target persons could choose between two or more offered modes. The use of reminders might be useful in solving this problem of competing risks. In the context of a multiple-panel study, this question was investigated by utilising longitudinal paradata from the fieldwork, as well as procedures of event history analysis that are adequate for the analysis of processes with competing risks. First, for a web survey as the initial mode and computer-assisted telephone interview (CATI) as the subsequent mode, it was found that the idea of a sequential mixed-mode plus "push-to-web" strategy does work even in the case of competing risks in the choice of a survey mode. Second, it was confirmed that reminders are a useful instrument for stimulating panellists to choose the running survey mode. Third, and finally, it was found that this feature of survey management is effective in countering panellists' procrastination in regard to responding to a survey.