From the Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY.
Division of Epidemiology and Biostatistics, School of Public Health, University of California, Berkeley, CA.
Epidemiology. 2020 Jul;31(4):523-533. doi: 10.1097/EDE.0000000000001191.
Randomized trials may have different effects in different settings. Moving to Opportunity (MTO), a housing experiment, is one such example. Previously, we examined the extent to which MTO's overall effects on adolescent substance use and mental health outcomes were transportable across the sites to disentangle the contributions of differences in population composition versus differences in contextual factors to site differences. However, to further understand reasons for different site effects, it may be beneficial to examine mediation mechanisms and the degree to which they too are transportable across sites.
We used longitudinal data from MTO youth. We examined mediators summarizing aspects of the school environment over the 10-15 year follow-up. Outcomes of past-year substance use, mental health, and risk behavior were assessed at the final timepoint when participants were 10-20 years old. We used doubly robust and efficient substitution estimators to estimate (1) indirect effects by MTO site and (2) transported indirect effects from one site to another.
Differences in indirect effect estimates were most pronounced between Chicago and Los Angeles. Using transport estimators to account for differences in baseline covariates, likelihood of using the voucher to move, and mediator distributions partially to fully accounted for site differences in indirect effect estimates in 10 of the 12 pathways examined.
Using transport estimators can provide an evidence-based approach for understanding the extent to which differences in compositional factors contribute to differences in indirect effect estimates across sites, and ultimately, to understanding why interventions may have different effects when applied to new populations.
随机试验在不同环境下可能具有不同的效果。“机遇住宅项目”（MTO）是一个住房实验，就是这样一个例子。在此之前，我们研究了 MTO 对青少年物质使用和心理健康结果的总体影响在多大程度上可以跨越各个地点进行推广，以厘清人口构成差异与环境因素差异对地点差异的贡献。然而，为了进一步了解不同地点效果的原因，检查中介机制及其在多大程度上可以跨越地点进行推广可能会有所帮助。
我们使用 MTO 青年的纵向数据。我们检查了在 10-15 年的随访过程中概括学校环境各个方面的中介变量。在参与者 10-20 岁时进行最后一次随访时，评估了过去一年的物质使用、心理健康和风险行为的结果。我们使用双重稳健和有效的替代估计量来估计（1）MTO 地点的间接效应和（2）从一个地点到另一个地点的传输间接效应。
在芝加哥和洛杉矶之间，间接效应估计值的差异最为明显。使用传输估计量来解释基线协变量、使用优惠券搬家的可能性以及中介变量分布方面的差异，可以部分或完全解释在 12 个路径中的 10 个路径中观察到的间接效应估计值的地点差异。
使用传输估计量可以为理解构成因素差异对不同地点间接效应估计值的差异程度提供一种循证方法，最终为理解为什么干预措施在应用于新人群时可能会产生不同的效果提供了依据。
