Basu Anirban, Heckman James J, Navarro-Lozano Salvador, Urzua Sergio
Section of General Internal Medicine, Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
Health Econ. 2007 Nov;16(11):1133-57. doi: 10.1002/hec.1291.
Instrumental variable (IV) methods are widely used in the health economics literature to adjust for hidden selection biases in observational studies when estimating treatment effects. Less attention has been paid in the applied literature to the proper use of IVs if treatment effects are heterogeneous across subjects and individuals select treatments based on expected idiosyncratic gains or losses from treatments. In this paper we compare conventional IV analysis with alternative approaches that use IVs to estimate treatment effects in models with response heterogeneity and self-selection. Instead of interpreting IV estimates as the effect of treatment at an unknown margin of patients, we identify the marginal patients and we apply the method of local IVs to estimate the average treatment effect and the effect on the treated on 5-year direct costs of breast-conserving surgery and radiation therapy compared with mastectomy in breast cancer patients. We use a sample from the Outcomes and Preferences in Older Women, Nationwide Survey which is designed to be representative of all female Medicare beneficiaries (aged 67 or older) with newly diagnosed breast cancer between 1992 and 1994. Our results reveal some of the advantages and limitations of conventional and alternative IV methods in estimating mean treatment effect parameters.
在估计治疗效果时，工具变量（IV）方法在健康经济学文献中被广泛用于调整观察性研究中隐藏的选择偏差。如果治疗效果在不同个体之间存在异质性，且个体根据治疗预期的特殊收益或损失来选择治疗方法，那么应用文献中对工具变量的正确使用关注较少。在本文中，我们将传统的IV分析与使用IV来估计具有反应异质性和自我选择模型中治疗效果的替代方法进行比较。我们不是将IV估计值解释为在未知患者边际上的治疗效果，而是识别边际患者，并应用局部IV方法来估计平均治疗效果以及乳腺癌患者保乳手术和放射治疗与乳房切除术相比对5年直接成本的治疗效果。我们使用了来自“老年女性结局与偏好全国性调查”的样本，该调查旨在代表1992年至1994年间所有新诊断为乳腺癌的女性医疗保险受益人（年龄67岁及以上）。我们的结果揭示了传统IV方法和替代IV方法在估计平均治疗效果参数方面的一些优点和局限性。
