Meta-analyses are commonly performed based on random-effects models, while in certain cases one might also argue in favour of a common-effect model. One such case may be given by the example of two "study twins" that are performed according to a common (or at least very similar) protocol. Here we investigate the particular case of meta-analysis of a pair of studies, e.g. summarizing the results of two confirmatory clinical trials in phase III of a clinical development programme. Thereby, we focus on the question of to what extent homogeneity or heterogeneity may be discernible, and include an empirical investigation of published ("twin") pairs of studies. A pair of estimates from two studies only provides very little evidence on homogeneity or heterogeneity of effects, and ad-hoc decision criteria may often be misleading.

翻译：基于随机效应模型的荟萃分析广泛应用，但在某些情况下，共同效应模型同样具有合理性。例如，两项遵循相同（或至少高度相似）试验方案的“双胞胎研究”可能就属于此种情况。本文聚焦于一对研究的荟萃分析特例（如临床开发计划III期两个确证性临床试验结果的汇总），重点探讨可识别的同质性或异质性程度，并对已发表的（“双胞胎”）研究对进行实证分析。研究表明，仅凭两项研究的估计值对效应量的同质性或异质性提供的证据极为有限，而事后决策标准往往可能产生误导。