Prepaid monetary incentive effects on mail survey response

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Abstract

Increasing mail survey response using monetary incentives is a proven, but not always cost-effective, method in every population. This paper tackles the questions of whether it is worth using monetary incentives and the size of the inducement by testing a regression model of the impact of prepaid monetary incentives on response rates in consumer and organizational mail surveys. The results support their use and show that the inducement value makes a significant impact on the effect size. Importantly, no significant differences were found between consumer and organizational populations.

Introduction

Methods of inducing higher response rates to mail surveys in order to reduce attendant problems of inadequate sample sizes and nonresponse bias continue to receive attention in the literature Jobber and O'Reilly, 1998, Angur and Nataraajan, 1995, Schneider and Johnson, 1995. In particular, prepaid monetary incentives have been studied and relatively consistent positive results have been reported in both consumer and organizational surveys (see Table 1, Table 2). However, this method can add significant cost to a project and there have been few systematic attempts to model the effects of different incentive sizes on response rates over a number of studies. A small sample size and the failure to distinguish between consumer and organizational populations limited one exception, a study by Jobber and Saunders (1988). Thus, little is known about the relationship between the size of the incentive and the size of the increased response. For example, “in the United States, a sum of 25¢ has been found to yield a substantial increase in response, whereas larger amounts bring in little more” (Moser and Kalton, 1976), while other authors suggest that 40¢ is the optimum amount (Armstrong, 1975). Furthermore, we do not know whether this relationship will be the same in widely different populations, e.g., between consumers and organizational respondents, as there is some evidence of differential inducement effects being observed (Jobber, 1986). Organisational respondents are likely to require higher incentives to affect the same change in response due to the competing demands placed on respondents' working day, the value they place on their time, and, possibly, their perception of the value of the information to the survey sponsor. Thus:

Hypothesis 1

Organizational and consumer respondents respond differently to monetary incentives.

Theoretical support for using prepaid monetary incentives is provided by the norm of reciprocity of Gouldner (1960), which states that people are more likely to help those who have helped them in some way. Giving a prepaid incentive builds a psychological obligation to reciprocate that is fulfilled by completing and returning the questionnaire. Respondent compliance might also increase because of uncomfortable levels of cognitive dissonance being created by accepting the incentive without responding (Festinger, 1957). To throw the money away would be wasteful, to accept it without completing the questionnaire would seem dishonest, and to return the money to the sender would involve fruitless effort (Furse and Stewart, 1982). Thus, the simplest method of dispelling any dissonance is compliance. Although Moser and Kalton (1976) and Armstrong (1975) argue that it is the giving of an incentive, not its value, that increases response rate, other studies have shown response to increase significantly with larger incentives (e.g., James and Bolstein, 1990). Thus:

Hypothesis 2

Response rates increase as the value of the prepaid monetary incentive increases.

The major objective of this study was to devise a statistical model to examine the cost-effectiveness of incentive size on mail survey response in consumer and organizational populations. This will facilitate a comparison with the results of an earlier study by Jobber and Saunders (1988) based on 16 experiments conducted prior to 1986. In doing this, we shall examine experimental evidence since 1975 to test the two hypotheses.

Section snippets

Modelling prepaid incentives and response

The database used in this study was obtained from 30 experiments into the effect of prepaid monetary incentives conducted since 1975 (see Table 1, Table 2). As the studies are drawn from different years, it is necessary to standardize the economic value of each incentive. The 1994 dollar was used as the base (no studies were found after 1994) and the average annual rate of increase in US consumer prices for the period 1975–1999 (source: International Monetary Fund, 1999) was employed to

Results

The results of the multiple regression analysis are shown in Table 3. The model was statistically significant (P<.05) with a correlation coefficient of .40. The coefficient for amended incentive value was statistically significant (P<.05) and the intercept value of 15.24 (P<.001) indicated that the act of enclosing an incentive had a substantial impact on response rate. The coefficient for type of survey was not statistically significant, indicating that the impact of a monetary incentive did

Discussion

The findings did not support Hypothesis 1 that organizational and consumer respondents respond differently to monetary incentives. However, Hypothesis 2, that response rates increase as the value of the prepaid monetary incentive increases, was supported.

The regression equation expresses the following: that inclusion of any incentive, regardless of amount, raises the response rate by an average of 15% across all the studies in this analysis. The size of the incentive had an additional effect at

Conclusion

The study by Jobber and Saunders (1988) supported the use of monetary incentives but concluded that incentive value made an insignificant contribution to the model. However, their work used a relatively small number of monetary incentive experiments. The addition of the 15 experiments conducted since then provides a more robust data set from which to draw conclusions. The new model once again confirms the efficacy of using monetary incentives to increase response to mail surveys, but now

Acknowledgements

The authors acknowledge the helpful comments and assistance of the reviewers and Damian Ward, University of Bradford, whose suggestions for revising the manuscript were extremely useful and gratefully received.

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