We examine a potential self-selection bias in different samples of experimental subjects depending on the payment scheme offered in the recruiting process. We ran four field experiments in which undergraduate students in a microeconomics course were invited to voluntarily set their own goal for the final exam. They were informed that they would be given a monetary reward (else nothing) if their actual grade were higher than or equal to their goal. Rewards were an increasing (quadratic) function of the goal. We aimed at studying whether subjects’ willingness to participate in the experiment depends on their expected performance under different advertised 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 nonparticipants in order to analyze sample-sorting effects. We find that when a rank-order tournament is offered alone or in combination with another reward mechanism, high-performing students are more likely than low-performing ones to participate in the experiment.

中文翻译：

---

实地实验中的自我选择偏差：不同支付方案下的招募对象

我们根据招聘过程中提供的付款方案检查不同实验对象样本中潜在的自我选择偏差。我们进行了四次实地实验，邀请参加微观经济学课程的本科生自愿为期末考试设定自己的目标。他们被告知，如果他们的实际成绩高于或等于他们的目标，他们将获得金钱奖励（否则没有）。奖励是目标的递增（二次）函数。我们的目的是研究受试者参与实验的意愿是否取决于他们在不同广告奖励标准下的预期表现，例如排名锦标赛和计件工资。鉴于对未来业绩的判断与之前的业绩密切相关，当前学术课程的期中考试成绩在参与者和非参与者之间进行比较，以分析样本分类效果。我们发现，当单独提供排名锦标赛或与其他奖励机制相结合时，表现优异的学生比表现不佳的学生更有可能参与实验。