The clustered observational study (COS) design is the observational study counterpart to the clustered randomized trial. In a COS, a treatment is assigned to intact groups, and all units within the group are exposed to the treatment. However, the treatment is non-randomly assigned. COSs are common in both education and health services research. In education, treatments may be given to all students within some schools but withheld from all students in other schools. In health studies, treatments may be applied to clusters such as hospitals or groups of patients treated by the same physician. In this manuscript, we study the identification of causal effects in clustered observational study designs. We focus on the prospect of differential selection of units to clusters, which occurs when the units' cluster selections depend on the clusters' treatment assignments. Extant work on COSs has made an implicit assumption that rules out the presence of differential selection. We derive the identification results for designs with differential selection and that contexts with differential cluster selection require different adjustment sets than standard designs. We outline estimators for designs with and without differential selection. Using a series of simulations, we outline the magnitude of the bias that can occur with differential selection. We then present two empirical applications focusing on the likelihood of differential selection.
翻译:集束观察研究(COS)设计是集束随机试验的观察研究。在集束随机试验中,对集束观察研究(COS)设计进行相应的观察研究。在集束观察试验中,对整群的组别进行治疗,对整群群别进行治疗,对组内所有单位都进行治疗。然而,这种治疗是非随机的。COS在教育和卫生服务研究中是常见的。在教育中,对一些学校的所有学生进行治疗,但对其他学校的所有学生不给予治疗。在健康研究中,治疗可适用于诸如医院或由同一医生治疗的病人组群等群,治疗。在这份手稿中,我们研究集群观察研究分类研究设计中的因果关系。我们注重对组组别进行差别选择的前景,当组别的选择取决于组群的治疗任务时,这种选择就会产生差别。关于COS的扩展工作隐含的假设是,排除有差别的选择。我们得出有差别的设计结果,而有差别的组别选择环境需要不同于标准的设计。我们概述了与差别选择的估测算师。我们用两个模型,我们用不同的选择差别选择的可能性。我们用不同的方法来区分。