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As mobile phone surveys are gaining popularity among researchers and practitioners in international development, one primary challenge is improving survey response and completion rates. A common solution is to provide monetary compensation to respondents. This paper reports on our experience with using incentives with a mobile phone survey conducted in Ghana and Tanzania in June 2015.
We find that extrinsic incentives – transfers of airtime – improve survey completion rates by roughly 6 to 8 percentage points. We also find that an SMS notification, aimed at increasing intrinsic motivation to complete the survey, has a comparable positive effect. Considering three levels of compensation (airtime transfers), we find that the supply curve of completed surveys appears to be fairly inelastic. In other words, small amounts of incentives have a similar effect as larger incentives. We also find little evidence of the extrinsic incentives skewing the demographics of the completed samples. However, we do find some evidence that the SMS treatment may have skewed the sample toward wealthier and more educated respondents. Finally, we found that the cost per completed response is not substantially less for every incentive or combination of incentives, compared to the group that did not receive any incentives.
Considering these results, we would recommend the consideration of modest monetary compensation as a way of increasing response and completion rates. Nonetheless, a complete lack of extrinsic incentives may remain the most cost effective way to gather completed responses without any associated risk of skewing the survey sample. However, if higher completion rates are desired, a small monetary compensation would be most cost effective with lower risks of biasing the completed sample