Understanding the effects of group composition by risk for violence. Experimental evidence from El Salvador
中文摘要
全球有1.5亿青少年报告曾在学校及其周边遭受或参与同伴间暴力。课后项目（ASPs）已成为缓解这一风险的一项策略，但基于暴力风险的同伴群体构成会如何影响课后项目的有效性？为回答这一问题，我在萨尔瓦多开展了一项随机实验，将青少年分配至对照组，或ASP内的同质同伴组与异质同伴组。我发现，同质组与异质组之间的平均差异有限。这种差异的缺失可由群体构成对基线暴力倾向不同的学生产生差异化影响来解释：异质处理使最脆弱的学生受益，同时不会损害最不易受伤害的学生。此外，群体构成要素的相反效应也发挥了作用：同伴暴力风险的均值越高，结果越差；而方差越大，结果越好。这些发现对公共政策具有重要意义，为暴力减少项目的最优群体构成提供了启示。
Abstract
Globally, 150 million adolescents report experiencing or engaging in peer-to-peer violence in and around schools. After-school programs (ASPs) have emerged as a strategy to mitigate this risk, but how does the peer group composition, based on the risk of violence, influence an ASP’s effectiveness? To address this question, I conducted a randomized experiment in El Salvador, assigning youths to a control group, homogeneous peer groups, or heterogeneous peer groups within an ASP. I find that there are limited average differences between the homogeneous and heterogeneous groups. This lack of differences is explained by the differential impacts of group composition based on students’ baseline propensity for violence: the heterogeneous treatment benefits the most vulnerable students and does not harm the least vulnerable. Additionally, the opposing effects of group composition components play a role: a higher mean of peers’ risk for violence worsens outcomes, while a higher variance improves them. These findings have important implications for public policy, offering insights into optimal group composition for violence reduction programs.