title: The effect of friend selection on social influences in obesity.
abstract: We present an agent-based model of weight choice and peer selection that simulates the effect of peer selection on social multipliers for weight loss interventions. The model generates social clustering around weight through two mechanisms: a causal link from others' weight to an individual's weight and the propensity to select peers based on weight. We simulated weight loss interventions and tried to identify intervention targets that maximized the spillover of weight loss from intervention participants to nonparticipants. Social multipliers increase with the number of intervention participants' friends. For example, when friend selection was based on a variable exogenous to weight, the weight lost among non-participants increased by 23% (14.3lb vs. 11.6lb) when targeting the most popular obese. Holding constant the number of participants' friends, multipliers increase with increased weight clustering due to selection, up to a point. For example, among the most popular obese, social multipliers when matching on a characteristic correlated with weight (1.189) were higher than when matching on the exogenous characteristic (1.168) and when matching on weight (1.180). Increased weight clustering also implies more obese "friends of friends" of participants, who reduce social multipliers.
authors.affiliation: Health Policy and Management, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, 1101B McGavran-Greenberg, 135 Dauer Dr., CB 7411, Chapel Hill, NC 27599-7411, USA. Electronic address: justintrogdon@unc.edu.
authors.forename: Justin G
authors.initials: JG
authors.lastname: Trogdon
authors.affiliation: Public Health Economics Program, RTI International, 3040 Cornwallis Road, Research Triangle Park, NC 27709, USA. Electronic address: ballaire@rti.org.
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Allaire
mesh_terms: D005247:Feeding Behavior; D005260:Female; D033062:Friends / Q000523:psychology*; D006801:Humans; D008297:Male; D009765:Obesity / Q000523:psychology*; D010379:Peer Group; D012015:Reference Standards; D012944:Social Support; D015431:Weight Loss
keywords: Agent-based model; Obesity; Peer effects; Social multiplier