中文摘要
与高能力同伴的接触会带来正向的学习外部性, 但同时也会因序数能力排名较低而降低学生的学业自我概念。我们证明, 由此导致线性均值 (linear-in-means) 参数识别的是一个复合 (即简化式) 效应。我们利用两个随机将学生分组的实验数据来说明这一问题的实证相关性。我们发现, 在包含排名的模型中估计出的平均同伴能力的结构效应, 远大于省略排名时所得到的简化式效应。这一发现在非线性及异质性同伴效应模型中同样成立, 并有助于厘清能力分班政策效应背后的机制。
Abstract
Exposure to high-ability peers entails positive learning externalities, but it also decreases students’ academic self-concept because of lower ordinal ability rank. We show that, as a result, the linear-in-means parameter identifies a composite (i.e., reduced form) effect. We illustrate the empirical relevance of this issue using data from two experiments that randomly assign students to groups. We find that the structural effect of mean peer ability estimated by a model that includes rank is much larger than the reduced form effect obtained when rank is omitted. This finding also holds in non-linear and heterogeneous peer effects models and helps clarify the mechanisms behind the effects of ability tracking policies.