Chapter 9 302 behaviour change). Recent evidence suggests that choice between incentives may be beneficial for student selecting into different grading schemes for a series of small exercises as part of a course.37 This may be interpreted as being in line our results. Arguably, students are able to anticipate the effort needed and benefits accrued from completing coursework on time, which would explain why as in our study, Incekara-Hafalir et al.37 find beneficial effects of choice. Reward vs. deposit-based incentives of different sizes The second key contrast in this study was between reward- and deposit-based incentives of different sizes. In particular, we compared effectiveness of these incentive schemes in those randomly assigned to them, as this avoids selfselection. We find that respondents were slightly less likely to show up for the next session of our experiment if they were assigned to deposit-based incentives. This appears to be in line with the low attractiveness of deposit-based incentives observed in earlier work, in which voluntary take-up was typically low,21, 22, 24 however this effect was not statistically significant. Importantly, effort provision was not affected by the type of incentive scheme respondents were assigned to, and as a result respondents earned less when they were randomly assigned to deposit-based incentives. This finding is in contrast to work by Patel et al.18 who found larger effectiveness for deposit-based incentives (compared to rewardbased incentives) for physical exercise. On the other hand, our null-result is in line with findings by Halpern et al. for smoking cessation.27 Hence, it appears the use of deposit-based incentives is beneficial compared to not using incentives at all,22, 24, 28 but it remains unclear if deposit-based incentives outperform incentives that do not involve losses. Future work may compare reward- and deposit-based incentives in a design that also includes a control condition without incentives to further explore this issue. Furthermore, our study included incentives of different sizes. Increasing reward size by 50% and 150% significantly increased persistence by ~16% and 34% respectively, which seems to suggest some degree of diminishing sensitivity to increasing reward size. This finding is in contrast to de Araujo et al.47 who find that persistence on slider task is largely insensitive to reward sizes. We do find that deposit-based incentives combined with low payments seem to yield a higher chance of drop-out (see Appendix C), which may suggest take-up of deposit-based incentives take-up can be increased by increasing total reward size.
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