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Background: Homophily is the tendency to associate with friends similar to ourselves. This study explored the effects of homophily on team formation in a physical activity challenge in which “captains” signed up their Facebook friends to form teams. Methods: This study assessed whether participants (n = 430) were more similar to their teammates than to nonteammates with regard to age, sex, education level, body mass index, self-reported and objectively measured physical activity, and negative emotional states; and whether captains were more similar to their own teammates than to nonteammates. Variability indices were calculated for each team, and a hypothetical variability index, representing that which would result from randomly assembled teams, was also calculated. Results: Within-team variability was less than that for random teams for all outcomes except education level and depression, with differences (SDs) ranging from +0.15 (self-reported physical activity) to +0.47 (age) (P < .001 to P = .001). Captains were similar to their teammates except in regard to age, with captains being 2.6 years younger (P = .003). Conclusions: Results support hypotheses that self-selected teams are likely to contain individuals with similar characteristics, highlighting potential to leverage team-based health interventions to target specific populations by instructing individuals with risk characteristics to form teams to help change behavior.
Edney, Olds, Curtis, and Maher are with the School of Health Sciences, University of South Australia, Adelaide, SA, Australia. Ryan is with Commonwealth Scientific and Industrial Research Organisation, Adelaide, SA, Australia. Plotnikoff is with the Priority Research Centre for Physical Activity and Nutrition, The University of Newcastle, Newcastle, NSW, Australia. Vandelanotte is with Physical Activity Research Group, Central Queensland University, Rockhampton, QLD, Australia.