Paying none, some or all? Between-subject random incentives and preferences towards risk and time

In the context of risk and time preferences, the within-subject random incentive system (Within-RIS) is the standard real-incentive mechanism in economic experiments: each subject has one choice randomly selected for payment. In a variation, Within-RIS is applied to a fraction of subjects only: each subject has a probability π of being selected and has one choice randomly selected for payment. This paper assesses the validity of this mechanism called the hybrid random incentive system (Hybrid-RIS) by investigating if/how the selection probability affects elicited risk and time preferences. We report an experiment conducted with 335 subjects across four treatments, varying the selection probability to 0, 0.1, 0.5, and 1. Using raw data statistics and structural estimations of preference parameters, we find that elicited time preferences remain stable, while risk aversion is lower when the selection probability is null. However, there are no significant differences among the non-null selection probabilities. These findings suggest that Hybrid-RIS does not distort elicited risk and time preferences.