This paper reports a series of experiments designed to evaluate how the advertised participation payment impacts participation rates in laboratory experiments. Our initial goal was to generate variation in the participation rate as a means to control for selection bias when evaluating treatment effects in common laboratory experiments. Initially, we varied the advertised participation payment to 1734 people from $\mathrm{\$}5$ to $\mathrm{\$}15$ using standard email recruitment procedures, but found no statistical evidence this impacted the participation rate. A second study increased the advertised payment up to $\mathrm{\$}100$. Here, we find marginally significant statistical evidence that the advertised participation payment affects the participation rate when payments are large. To combat skepticism of our results, we also conducted a third study in which verbal offers were made. Here, we found no statistically significant increase in participation rates when the participation payment increased from $\mathrm{\$}5$ to $\mathrm{\$}10$. Finally, we conducted an experiment similar to the first one at a separate university. We found no statistically significant increase in participation rates when the participation payment increased from $\mathrm{\$}7$ to $\mathrm{\$}15$. The combined results from our four experiments suggest moderate variation in the advertised participation payment from standard levels has little impact on participation rates in typical laboratory experiments. Rather, generating useful variation in participation rates likely requires much larger participation payments and/or larger potential subject pools than are common in laboratory experiments.

This paper reports the results of an experiment designed to study how subjects’ decision making may be affected by the timing of participation payments (or show-up fees). The experiment follows Davis et al. (J. Econ. 30:69-95, 2004) where subjects were asked to make a sequential purchase decision and were given the opportunity to purchase information about the value of a good prior to a decision to purchase the good itself. There, subjects purchased information less often than expected which was interpreted as risk-seeking behavior. Here, we test a payment hypothesis by varying the timing of the participation payment. Payment of a show-up fee before the decision-making stages of the experiment increases information purchase, which we interpret as an increase in risk-averse behavior.