Original article Do peer social relationships mediate the harmful effects of a housing mobility experiment on boys' risky behaviors? Nicole M. Schmidt, PhD a, * , Naomi Harada Thyden, SM b , Huiyun Kim, PhD a , Theresa L. Osypuk, SD, SM a, b a Minnesota Population Center, University of Minnesota, Minneapolis b Department of Epidemiology and Community Health, University of Minnesota School of Public Health, Minneapolis article info Article history: Received 18 October 2019 Accepted 18 May 2020 Available online xxx Keywords: Risky behaviors Mediation Peers Randomized controlled trial Mobility Public housing Adolescence abstract Purpose: The purpose of this study was to understand why a housing mobility experiment caused harmful effects on adolescent boys' risky behaviors. Methods: Moving to Opportunity (MTO) (1994e2010) randomly assigned volunteer families to a treatment group receiving a Section 8 rental voucher or a public housing control group. Our outcome was a global risky behavior index (RBI; measured in 2002, n ¼ 750 boys) measuring the fraction of 10 items the youth engaged in, 6 measuring past 30-day substance use and 4 measuring recent risky sexual behavior. Potential mediators (measured in 2002) included peer social relationships (e.g., peer drug use, peer gang membership). Results: The voucher treatment main effect on boys' RBI was harmful (B (SE) ¼ 0.05 (0.02), 95% CI 0.01, 0.08), and treatment marginally increased having friends who used drugs compared to controls (B (SE) ¼ 0.67 (0.23), 95% CI 0.22, 1.12). Having friends who used drugs marginally mediated the MTO treatment effect on RBI (indirect effect: B (SE) ¼ 0.02(.01), 95% CI 0.002, 0.04), reducing the total treatment effect by 39%. Conclusions: Incorporating additional supports into housing voucher programs may help support teenage boys who experience disruptions to their social networks, to buffer potential adverse conse- quences of residential mobility. © 2020 Elsevier Inc. All rights reserved. Introduction Adolescent risky behaviors, such as substance use and risky sex- ual behavior, may harm health and social development over the life course [1]. Given the tendency for these behaviors to escalate and persist into adulthood [2], early identification of the causes of risky behaviors is important for minimizing their public health impacts [3e5]. Previous observational studies on residential mobility suggest that frequent residential moves are a stressor for children [6e8], leading to problems during adolescence. Residential mobility nega- tively impacts risky behaviors [9,10], as well as delinquency [11], behavior problems [12], recidivism [13], and education [6]. However, this literature might be confounded by factors that affect mobility choices, such as family socioeconomic status. A growing literature examining the effects of residential mobility and neighborhood context on health leverages quasi-experimental and experimental data to overcome the potential for confounding in observational data [14]. Much of this literature relies on the Moving to Opportunity (MTO) demonstration. MTO randomly assigned low- income families in public housing to receive a voucher to be used in neighborhoods with less than 10% poverty, receive an unrestricted voucher, or remain in public housing [15]. The goal was to reduce concentrated poverty and improve economic outcomes for low- income families [16]. Interim survey findings (4e7 years after randomization) documented beneficial effects of mobility for adolescent girls, with reductions in psychological distress, lifetime marijuana use, lifetime smoking, and risky behaviors in the treatment group versus controls [17e21]. Boys experienced harmful effects, with increases in psychological distress, behavior problems, smoking, and risky behaviors, compared to controls [17e21]. Moreover, the harmful effects on boys' risky behaviors were concentrated among boys 10 years of age or older at baseline [21]. The final survey findings (10e15 years after randomization) showed, among a younger cohort of adolescents, decreased psychological distress, serious behavioral/emotional problems, and alcohol use for girls, but increased lifetime smoking for boys and the total sample [22]. * Corresponding author. Minnesota Population Center, University of Minnesota, 225 19th Avenue South, 50 Willey Hall, Minneapolis, MN 55455. Tel.: 612-624- 5818; fax: 612-626-8375. E-mail address: schmidtn@umn.edu (N.M. Schmidt). Contents lists available at ScienceDirect Annals of Epidemiology https://doi.org/10.1016/j.annepidem.2020.05.007 1047-2797/© 2020 Elsevier Inc. All rights reserved. Annals of Epidemiology xxx (xxxx) xxx Please cite this article as: Schmidt NM et al., Do peer social relationships mediate the harmful effects of a housing mobility experiment on boys' risky behaviors?, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2020.05.007