Experimental designs in the social sciences have received increasing attention due to their power to produce causal inferences. Nevertheless, experimental research faces limitations, including limited external validity and unrealistic treatments. We propose combining qualitative fieldwork and experimental design iteratively—moving back-and-forth between elements of a research design—to overcome these limitations. To properly evaluate the strength of experiments researchers need information about the context, data, and previous knowledge used to design the treatment. To support our argument, we analyze 338 pre-analysis plans submitted to the Evidence in Governance and Politics repository in 2019 and the design of a study on public opinion support for punitive policing practices in Montevideo, Uruguay. The paper provides insights about using qualitative fieldwork to enhance the external validity, transparency and replicability of experimental research, and a practical guide for researchers who want to incorporate iteration to their research designs.

社会科学中的实验设计因其产生因果推论的能力而受到越来越多的关注。然而，实验研究面临局限性，包括有限的外部有效性和不切实际的治疗。我们建议迭代地结合定性实地工作和实验设计——在研究设计的元素之间来回移动——以克服这些限制。为了正确评估实验的强度，研究人员需要有关用于设计治疗的背景、数据和先前知识的信息。为了支持我们的论点，我们分析了 2019 年提交给治理和政治证据库的 338 份预分析计划，以及一项关于公众舆论支持乌拉圭蒙得维的亚惩罚性警务实践的研究设计。