The long-term effect of material incentives on participation in online panels

A five-wave experiment examined the influence of incentives on response in online panels. One group of panelists was sent an advance gift after registering with the panel; the other group did not receive a gift. For participating in the studies, half of the panelists were repeatedly offered redeemable loyalty points. The others were offered inclusion in cash lotteries. At the outset, the advance gift significantly increased participation, but this effect dwindled linearly throughout the waves of the study. Initially there was no difference in response between people with loyalty points and those offered to be included in the cash lottery. Over time, however loyalty points relative to the cash lotteries became more attractive. In wave 1, the advance gift was especially useful when combined with the lottery. This effect faded in the course of the longitudinal study. Low-income panelists were more susceptible to the advance gift.