research on incentives focusing on findings largely drawn from randomized experiments. She examined the effects of incentives on response quality, sample composition, and response distributions. She noted that incentives have been found to reduce nonresponse rates, primarily by reducing refusals, but that little is known about their effect on nonresponse bias.

There are a number of answers to the question of why people respond to surveys. All theories of survey response emphasize the role of incentives in motivating behavior, though these need not be monetary incentives. Singer noted that results from responses to open-ended questions suggest that there are three main reasons for responding to surveys: altruistic reasons (e.g., wanting to be helpful); egoistic reasons (e.g., monetary incentives); and reasons associated with aspects of the survey (e.g., topic interest, trust in the sponsor). Both theory and observation confirm the importance of incentives for participation in surveys.

Effects on Cooperation

Incentives improve cooperation (Church, 1993; Singer and Ye, 2013). For example, Mann et al. (2008) reported that in a longitudinal study of young adults, parents receiving incentives of $1 or $2 were more likely than those receiving no incentives to provide addresses for their adult children, and children of parents receiving incentives responded more quickly to the survey.

In another study, Holbrook et al. (2008) analyzed 114 RDD surveys between 1996 and 2005 and found, after controlling for other variables, that incentives were significantly associated with higher response rates, with the effect due mainly to a reduction in refusals (with no change in contact rates).

Beydoun et al. (2006) compared the results of unconditional (prepaid) and conditional (promised) incentives on tracing and contact rates in a sample of Iowa postpartum women. The unconditional incentive rates were slightly higher than were the conditional rates, and the highest rates were attained when the incentives were combined.

Effects in Mail Surveys

One meta-analysis by Church (1993) found that prepaid incentives yielded significantly higher response rates to mail surveys than promised or no incentives, that they yielded higher response rates than gifts, and that response rates increased with increasing amounts of money. In another meta-analysis, Edwards et al. (2002) reported similar results.



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