Belief Elicitation: A Horse Race among Truth Serums

In survey studies, probabilistic expectations about uncertain events are typically elicited by asking respondents for their introspective beliefs. If more complex procedures are feasible, beliefs can be elicited by incentive compatible revealed preference mechanisms (“truth serums”). Various mechanisms have been proposed in the literature, which differ in the degree to which they account for respondents’ deviations from expected value maximization. In this paper, we pit non-incentivized introspection against five truth serums, to elicit beliefs in a simple two-player game. We test the internal validity (additivity and predictive power for own behavior), and the external validity (predictive power for other players’ behavior, or accuracy) of each method. We find no differences among the truth serums. Beliefs from incentivized methods are better predictors of subjects’ own behavior compared to introspection. However, introspection performs equally well as the truth serums in terms of accuracy and additivity.