The LISS panel (Longitudinal Internet Studies for the Social sciences) is an online panel which is based on a true probability sample of households. Households that cannot otherwise participate are provided with a computer and Internet connection.

In the LISS panel we call respondents “sleepers” when they are still registered as panel members but have not completed any questionnaires for three consecutive months or longer. In a telephone sleeper study, we tried to find out how the sleeping panel members could be re-activated. Sleepers indicated that their main motivation to become a panel member was personal interest/curiosity, followed by the financial compensation and contribution to science. The majority gave a personal reason for not completing any questionnaires anymore. Less than 10% indicated that they would prefer mail or telephone interviews instead of online questionnaires.

The study included an experiment in which various additional compensations were offered, in combination with arguments that emphasized how important it is that all panel members participate. On average 41% of the interviewed sleepers restarted their participation for at least one month. The percentage varied between 28% and 50% in the different experimental conditions. With regard to long-term participation, 25% of the interviewed sleepers continued to participate for three months or longer after the interview. This percentage also varied across the conditions, from 19% to 31%. The experiment showed that the most efficient method to reactivate sleepers is to promise them 10 euro conditional on renewed participation.