工具变量估计的全匹配方法及其在疟疾对发育迟缓影响中的应用
Full Matching Approach to Instrumental Variables Estimation with Application to the Effect of Malaria on Stunting
摘要：
以往大多数关于疟疾和发育迟缓之间因果关系的研究都是通过基于回归的方法控制潜在混杂因素的研究，但这些研究可能因未观察到的混杂因素而存在偏倚。工具变量（IV）回归提供了一种控制未测量混杂因素的方法，在我们的情况下，镰状细胞性状可以用作工具。然而，为了使该工具有效，考虑测量的混杂因素可能仍然很重要。最常用的工具变量回归方法，两阶段最小二乘法，依赖于测量混杂因素的影响的参数假设来解释它们。此外，两阶段最小二乘法在协变量平衡和受试者权重方面缺乏透明度，并且不会使研究人员对结果数据视而不见。为了解决这些缺点，我们提出了一种基于完全匹配的IV估计的替代方法。我们评估我们的新程序的模拟数据和真实数据的因果关系影响疟疾儿童发育迟缓。我们估计，镰状细胞性状儿童发育迟缓的风险比镰状细胞性状预防的疟疾发作平均次数减少0.22倍，这是疟疾对发育迟缓的重大影响（p值：0.011，95%CI：0.044，1）。
英文摘要：
Most previous studies of the causal relationship between malaria and stunting have been studies where potential confounders are controlled via regression-based methods, but these studies may have been biased by unobserved confounders. Instrumental variables (IV) regression offers a way to control for unmeasured confounders where, in our case, the sickle cell trait can be used as an instrument. However, for the instrument to be valid, it may still be important to account for measured confounders. The most commonly used instrumental variable regression method, two-stage least squares, relies on parametric assumptions on the effects of measured confounders to account for them. Additionally, two-stage least squares lacks transparency with respect to covariate balance and weighing of subjects and does not blind the researcher to the outcome data. To address these drawbacks, we propose an alternative method for IV estimation based on full matching. We evaluate our new procedure on simulated data and real data concerning the causal effect of malaria on stunting among children. We estimate that the risk of stunting among children with the sickle cell trait decrease by 0.22 times the average number of malaria episodes prevented by the sickle cell trait, a substantial effect of malaria on stunting (p-value: 0.011, 95% CI: 0.044, 1).
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