Experiments on Performance-related Pay and Stress: Evidence from a Cross-over Study, 2019

As described in the overarching funded project description, the focus of the research is to examine the relationship between performance-related pay and stress using experimental methods. Importantly, stress is measured here both subjectively (i.e. asking the stress level of participants) and objectively (i.e. collection of salivary cortisol).

The basic experiment is generally the same across all of the experiments in the project. Subjects are recruited by using a database at the university where the experiments took place. All experimental sessions happened at 1400 to control for the diurnal patterns of cortisol. Participants were also told to avoid exercising, smoking, drinking caffeine and eating two hours before the experiment since these also affect cortisol. During the experiment, participants are told generally about the experiment and enter a 10-minute relaxation period where they can colour in a mindfulness colouring page if they wish. Then they are asked questions about their subjective stress and a baseline cortisol measurement. Next, participants are given three example maths questions to complete in their own time and then allocated their employment contract. The performance-related pay (PRP) contract is piece rate based on the number of correct answers while the minimum performance contract (nonPRP) is a flat rate once ten questions are answered correctly. Then, participants are given 10 minutes to complete as many questions of maths problems (up to 50) without the use of a calculator. The computer screen gives the number of correct answers and for the nonPRP group, a banner is shown when they answer 10 questions correctly. After the task, a screen shows how much they earned from their performance, including the show up fee. Another measure of cortisol is taken and a survey administered to collect information on subjective stress and to collect demographic information. Participants had a 10 minute rest period of colouring after which a third cortisol sample was taken. Then participants had one final 10 minute rest period after which a fourth and final cortisol sample was taken. Finally, participants were called into the control room and given their payment.

In this first experiment, we want to establish the robustness of the relationship in two dimensions. First, we randomise the payment condition (either PRP or nonPRP) to ensure that we avoid problems of sample selection. Second, we utilise a cross-over design where a week after the initial experiment, we invited the participants back to the laboratory and switched conditions on the participants. This way, each participant serves as their own control, allowing us to control for individual heterogeneity in subjective and objective stress. Participants were paid a £5 participation fee, £5 if they met the minimum performance contract and were paid £0.20 for each correct answer when in the PRP contract. The findings, published in the Journal of Economic Behavior and Organization in 2021, showed that the PRP contract generated higher levels of cortisol and subjective stress.

如本资助项目总览描述所述，本研究的核心为采用实验方法探究绩效薪酬（performance-related pay, PRP）与压力之间的关联。值得注意的是，本研究同时从主观（即询问参与者的压力水平）与客观（即收集唾液皮质醇（salivary cortisol））两个维度对压力进行测量。

本项目所有实验的基础流程大体一致。实验参与者通过实验开展高校的受试者数据库招募。所有实验时段均定于14:00开展，以控制皮质醇的昼夜节律波动。同时告知参与者，需在实验前2小时内避免运动、吸烟、摄入咖啡因及进食，上述行为均会影响皮质醇水平。实验开始时，先向参与者简要介绍实验流程，随后进入10分钟的放松阶段，参与者可按需填写正念涂色页。之后，工作人员会询问参与者的主观压力水平，并采集基线唾液皮质醇样本。随后，先向参与者展示3道数学例题供其自行完成，再为其分配雇佣合约类型：绩效薪酬合约（PRP）为按正确答题数量计费的计件合约，而最低绩效合约（nonPRP）则在参与者答对10道题后支付固定报酬。之后，参与者需在10分钟内完成至多50道数学题，且不得使用计算器。电脑屏幕会实时显示正确答题数量；对于nonPRP组参与者，当其答对10道题时，屏幕将弹出提示横幅。任务结束后，屏幕将展示参与者本次实验的总收益，其中包含到场补贴。随后再次采集唾液皮质醇样本，并通过问卷调查收集参与者的主观压力水平与人口统计学信息。之后，参与者进入10分钟的涂色休息阶段，结束后采集第三份皮质醇样本。接着，参与者再进行最后一次10分钟休息阶段，之后采集第四份即最终一份皮质醇样本。最后，参与者被引导至控制室领取实验报酬。

在本次首轮实验中，我们旨在从两个维度验证该关联的稳健性：其一，我们对薪酬条件（PRP或nonPRP）进行随机化分配，以规避样本选择偏误问题；其二，我们采用交叉实验设计：在首轮实验结束一周后，邀请参与者返回实验室，并互换其此前的薪酬条件。通过该设计，每位参与者均可作为自身的对照组，从而能够控制主观与客观压力层面的个体异质性。本次实验中，参与者可获得5英镑的到场补贴，若达成最低绩效合约要求则额外获得5英镑，而在PRP合约条件下，每答对一道题可获得0.20英镑的报酬。本研究成果已于2021年发表于《经济行为与组织期刊（Journal of Economic Behavior and Organization）》，结果显示，PRP合约会导致更高的皮质醇水平与主观压力评分。