External validity in economic experiments: can students be used to approximate the behavior of farmers?

在对经济实验进行有意义的解释时，外部效度是最关键的方面之一。关键的问题是，实验观察到的行为对特定的现实环境和感兴趣的社会群体具有何种预测能力。这是一个尖锐的问题，因为为了方便起见，使用学生作为替代实验对象已经成为一种常见的做法。实验研究的稳健性和意义，特别是在学生中进行的实验研究，可能会受到一些问题的损害。第一个问题涉及在实验对象样本中观察到的行为影响的可复制性，这些影响取决于实验变化的条件。第二个问题是，实验设计本身是否适合让实验对象揭示他们的真实偏好，或者是否存在扭曲，例如由激励不足引起的社会可取性偏见。鉴于广泛使用学生作为实验对象，进一步的关注与结果的可转移性有关：我们能从学生群体的实验行为中科学地推断出感兴趣的社会群体的行为吗？从这些问题的整体来看，解决经济实验结果的普遍性的综合方法研究很少。关于在农业经济学中使用实验，目前还没有系统的研究来调查稳健性，特别是可转移性问题。在此背景下，本项目旨在找出“促进稳健性”的方法可以对实验结果做出更明智的解释。一方面，我们着眼于改进统计推断的新的经验和统计策略，例如预登记研究设计，考虑多个测试问题，以及进行功率分析和重复。从实验设计的角度，我们进一步研究了系统变化的激励是否以及如何影响行为。这是一个特别有趣的问题，因为与实验心理学家相反，实验经济学家认为，需要金钱激励才能使实验对象揭示他们的真实偏好。我们使用多期商业模拟游戏，让学生和农民都在两种情境下经营虚拟农场并做出生产计划决策，作为实验装置来研究以下问题：(1)在系统变化的激励下，学生和农民的行为是否存在差距或差距有多大？(2)哪些因素可以解释学生和农民之间最终观察到的行为差异？(3)研究预注册、多重检验、功效分析和复制等新策略对外部效度的贡献是什么？

External validity is one of the most crucial aspects in the meaningful interpretation of eco-nomic experiments. The critical question is which predictive power an experimentally observed behavior has for a particular real-world context and social group of interest. This is a poignant question because, for the sake of convenience, it has become common practice to use students as substitute experimental subjects. The robustness and meaningfulness of experimental studies, especially when conducted with students, can be impaired by a number of problems. The first one concerns the replicability of the behavioral effects that are observed in a sample of experimental subjects contingent on experimentally varied conditions. The second concern is whether the experimental design itself is suited for making experimental subjects reveal their true preferences, or whether distortions, such as a social desirability bias caused by insufficient incentives, linger. Given the widespread use of students as experimental subjects, a further concern is related to the transferability of results: what can we scientifically infer from the experimental behavior of the student population for the behavior of the social group of interest?Comprehensive methodological studies that address the generalizability of findings from economic experiments in the light of the entirety of these problems are scarce. With a view to the use of experiments in agricultural economics, no systematic studies are known that investigate the robustness and especially the transferability issue. Against this background, this project is aimed at finding out which contribution "robustness-promoting" approaches can make to a more informed interpretation of experimental findings. For one thing, we look at new empirical and statistical strategies for improving statistical inference, such as preregistering study designs, accounting for multiple testing problems, and carrying out power analyses and replications. With a view to experimental design, we furthermore study whether and how systematically varied incentives affect behavior. This is an especially interesting issue because experimental economists, contrary to experimental psychologists, contend that monetary incentives are needed to make experimental subjects reveal their true preferences.We use multi-period business simulation games, in which students and farmers alike run virtual farms and make production program decisions in two contexts, as experimental device to study the following questions: (1) Is there a gap, or how big is the gap, between students' and farmers' behavior contingent on systematically varied incentives? (2) Which factors can explain eventually observed behavioral differences between students and farmers? (3) Which contribution to external validity can be provided by new strategies such as the preregistration of studies, the consideration of multiple testing, and power analysis and replication?