The Perils of Peer Effects

Individual outcomes are highly correlated with group average outcomes, a fact often interpreted as a causal peer effect. Without covariates, however, outcome-on-outcome peer effects are vacuous, either unity or, if the average is defined as leave-out, determined by a generic intraclass correlation

个体结果与群体平均结果高度相关，这一事实常被解读为因果同伴效应（causal peer effect）。然而，若缺乏协变量（covariates），结果对结果的同伴效应则失去实质意义——要么等于1，要么在平均被定义为留一平均时，由一般组内相关（intraclass correlation）所决定。