In this paper we revisit some common recommendations regarding the analysis of matched-pair and stratified experimental designs in the presence of attrition. Our main objective is to clarify a number of well-known claims about the practice of dropping pairs with an attrited unit when analyzing matched-pair designs. Contradictory advice appears in the literature about whether or not dropping pairs is beneficial or harmful, and stratifying into larger groups has been recommended as a resolution to the issue. To address these claims, we derive the estimands obtained from the difference-in-means estimator in a matched-pair design both when the observations from pairs with an attrited unit are retained and when they are dropped. We find limited evidence to support the claims that dropping pairs helps recover the average treatment effect, but we find that it may potentially help in recovering a convex weighted average of conditional average treatment effects. We report similar findings for stratified designs when studying the estimands obtained from a regression of outcomes on treatment with and without strata fixed effects.

翻译：本文重新审视了在存在流失情况下，关于配对与分层实验设计分析的一些常见建议。我们的主要目标是澄清一系列广为人知的主张，这些主张涉及在分析配对设计时，是否应剔除含有流失单位的配对组。文献中出现了相互矛盾的建议，关于剔除配对组是有益还是有害，而将分层设计中的分组扩大则被推荐为解决此问题的方法。为验证这些主张，我们推导了在配对设计中，当保留含有流失单位的配对组观测值与剔除这类配对组时，通过均值差异估计量得到的估计目标。我们发现的证据有限，不足以支持剔除配对组有助于恢复平均处理效应的说法，但发现它可能有助于恢复条件平均处理效应的凸加权平均。对于分层设计，我们在研究是否包含分层固定效应的处理结果回归所得的估计目标时，报告了类似发现。