Randomized control trials are considered the pinnacle for causal inference. In many cases, however, randomization of participants in social work research studies is not feasible or ethical. This paper introduces the co-twin control design study as an alternative quasi-experimental design to provide evidence of causal mechanisms when randomization is not possible. This method maximizes the genetic and environmental sameness between twins who are discordant on an “exposure” to provide strong counterfactuals as approximations of causal effects. We describe how the co-twin control design can be used to infer causality and in what type of situations the design might be useful for social work researchers. Finally, we give advantages and limitations to the design, list a set of Twin Registries with data available after application, and provide an example code for data analysis.

随机对照试验被认为是因果推理的巅峰之作。然而，在许多情况下，将社会工作研究的参与者随机化是不可行的或不符合道德的。本文介绍了双胞胎对照设计研究作为一种替代的准实验设计，以在不可能进行随机化时提供因果机制的证据。这种方法最大化了在“暴露”上不一致的双胞胎之间的遗传和环境相同性，以提供强有力的反事实作为因果效应的近似值。我们描述了如何使用双胞胎控制设计来推断因果关系，以及该设计在什么类型的情况下可能对社会工作研究人员有用。最后，我们给出了设计的优点和限制，列出了一组 Twin Registries 以及应用后可用的数据，