Understanding Instrumental Variables in Models with Essential Heterogeneity
研究工具变量在本质异质性模型中的性质，这类模型假设个体对干预的反应不同且部分知晓自身反应，文中分析了多种结果模型并开发了检验方法。
This paper examines the properties of instrumental variables (IV) applied to models with essential heterogeneity, that is, models where responses to interventions are heterogeneous and agents adopt treatments (participate in programs) with at least partial knowledge of their idiosyncratic response. We analyze two-outcome and multiple-outcome models, including ordered and unordered choice models. We allow for transition-specific and general instruments. We generalize previous analyses by developing weights for treatment effects for general instruments. We develop a simple test for the presence of essential heterogeneity. We note the asymmetry of the model of essential heterogeneity: outcomes of choices are heterogeneous in a general way; choices are not. When both choices and outcomes are permitted to be symmetrically heterogeneous, the method of IV breaks down for estimating treatment parameters. Copyright by the President and Fellows of Harvard College and the Massachusetts Institute of Technology.