Instrumental Variables and the Search for Identification: From Supply and Demand to Natural Experiments
回顾工具变量方法从1920年代用于估计供需弹性，到后来纠正测量误差、减少遗漏变量偏误的发展历程，并讨论有效工具变量的特征，特别关注基于自然实验的工具变量。
Instrumental variables was first used in the 1920s to estimate supply and demand elasticities and later to correct for measurement error in single equation models. Recently, instrumental variables have been widely used to reduce bias from omitted variables in estimates of causal relationships. Intuitively, instrumental variables methods use only a portion of the variability in key variables to estimate the relationships of interest; if the instruments are valid, that portion is unrelated to the omitted variables. We discuss the mechanics of instrumental variables and the qualities that make for a good instrument, devoting particular attention to instruments derived from “natural experiments.”