We replicate an influential study of monetary incentive effects by Jamal and Sunder (1991) to illustrate the difficulties of drawing causal inferences from a treatment manipulation when other features of the experimental design vary simultaneously. We first show that the Jamal and Sunder (1991) conclusions hinge on one of their laboratory market sessions, conducted only within their fixed-pay condition, that is characterized by a thin market and asymmetric supply and demand curves. When we replicate this structure multiple times under both fixed pay and pay tied to performance, our findings do not support Jamal and Sunder's (1991) conclusion about the incremental effects of performance-based compensation, suggesting that other features varied in that study likely account for their observed difference. Our ceteris paribus replication leaves us unable to offer any generalized conclusions about the effects of monetary incentives in other market structures, but the broader point is to illustrate that experimental designs that attempt to generalize effects by varying multiple features simultaneously can jeopardize the ability to draw causal inferences about the primary treatment manipulation.

How to hire voluntary helpers? We shed new light on this question by reporting a field experiment in which we invited 2859 students to help at the ‘ESA Europe 2012’ conference. Invitation emails varied non-monetary and monetary incentives to convince subjects to offer help. Students could apply to help at the conference and, if so, also specify the working time they wanted to provide. Just asking subjects to volunteer or offering them a certificate turned out to be significantly more motivating than mentioning that the regular conference fee would be waived for helpers. By means of an online-survey experiment, we find that intrinsic motivation to help is likely to have been crowded out by mentioning the waived fee. Increasing monetary incentives by varying hourly wages of 1, 5, and 10 Euros shows positive effects on the number of applications and on the working time offered. However, when comparing these results with treatments without any monetary compensation, the number of applications could not be increased by offering money and may even be reduced.

We examine how monetary incentives and information about others’ dishonesty affect lying decisions and whether these two dimensions interact with each other. Our experiment consists of a repeated cheating game where we vary the monetary incentives (Low, High, and Very High) and information about others’ dishonesty (With or Without information). We find that dishonesty decreases when payoffs are Very High. Information has only a weak positive effect on average. Conditioning on beliefs, we find that those who overestimate (underestimate) cheating reduce (increase) dishonesty. Information and payoffs do not interact with each other.

Researchers typically use incentives (such as money or course credit) in order to obtain participants who engage in the specific behaviors of interest to the researcher. There is, however, little understanding or agreement on the effects of different types and levels of incentives used. Some results in the domain of statistical reasoning suggest that performance differences — previously deemed theoretically important — may actually be due to differences in incentive types across studies. 704 participants completed one of five variants of a statistical reasoning task, for which they received either course credit, flat fee payment, or performance-based payment incentives. Successful task completion was more frequent with performance-based incentives than with either of the other incentive types. Performance on moderately difficult tasks (compared to very easy and very hard tasks) was most sensitive to incentives. These results can help resolve existing debates about inconsistent findings, guide more accurate comparisons across studies, and be applied beyond research settings.