There is a ton of research investigating the effects of incentives on survey efforts: web surveys, paper questionnaires, phone interviews and in-person feedback forms, to name a few. However, there is a shortage of literature investigating the best way to go about offering incentives to individuals who may be involved in a longer survey.
Longitudinal surveys (or studies) sometimes take months or years for a person to complete. Many times longitudinal surveys involve a serious time commitment on the part of the participant, leading to higher attrition rates as people drop out of the research as the years go by.
So it would seem only natural that because of this extra effort on behalf of our participants, we would want to provide extra inventive to keep our market research sample sizes up as the project moves along. What's the best way to go about doing this? Well, although there isn't much literature on the topic, the meta-analysis that has been done can prove to be pretty useful.
The Journal of Official Statistics (JOS) published research that showed that splitting your total incentive amount per participant evenly over the total number of survey waves may be better than providing the whole incentive at one time.
For example if you have $50 to spend on each participant over a 5 year longitudinal study, it may be best to split that $50 into $10 pieces for each year of participation, rather than waiting until the 5 years are complete to give the participant their $50.
Tomorrow for our incentives for longitudinal surveys topic we will look at the benefits of using different types of incentives during different phases of your longitudinal research effort.