The Use of Instrumental Variables in Peer Effects Models
指出，在用同伴平均特征作为工具变量识别同伴效应时，必须将个体层面的工具变量作为解释变量纳入模型，否则会产生偏误。
Abstract Instrumental variables are often used to identify peer effects. This paper shows that instrumenting the ‘peer average outcome’ with ‘peer average characteristics’ requires the researcher to include the instrument at the individual level as an explanatory variable. We highlight the bias that occurs when failing to do this.