Self-selection bias in a field experiment: Recruiting subjects under different payment schemes

In this paper, we examine a potential self-selection bias in different samples of subjects depending on the payment scheme offered in the recruiting process. We ran four field experiments in which students enrolled in a microeconomics course were invited to set their own goal for the final exam of the course. Subjects were informed that they could be given a monetary reward if their grade were higher than or equal to their self-chosen goal. We aim to study whether subjects’ willingness to participate depends on their expected performance under diverse announced reward criteria, like a rank-order tournament and piece-rate pay. Given that judgments about future performance are closely tied to previous performance, the midterm exam scores from the current academic course are compared between participants and non-participants in order to analyze sample-sorting effects. We find that only when a rank-order tournament is offered, either exclusively or in combination with another type of payment mechanism, are high-performing students more likely to participate in the experiment than low-performing ones.