Physical Activity and Social Comparison: The Importance of Group Composition in an Employee Fitbit Intervention.

This study examined the impact of group composition of a 6-week group-based employee Fitbit intervention on daily physical activity steps. Group composition comprised heterogenous and homogeneous groupings based on variations in baseline high, medium, and low steppers. The intervention included weekly step leaderboard information, motivational and informative messages, and the ability to participate in group step challenges. Repeated measures analysis of variance (ANOVA) examined differences in change of steps across time, step-level groups (low, medium, and high), and group composition (low/high, similar, and mixed), and replicated with a subgroup of participants who participated in group step challenges. While group and step level did not emerge as significant interactions in the overall sample, when focused within the group step challenge subsample, relationships among time, the group composition, and participant step-level categories emerged. Overall, the greatest increases in steps occurred at the mid-point time period, among lower steppers, and within the low/high comparison group. This study provides evidence of the importance of group composition in physical activity interventions as well as the fidelity of intervention design in facilitating group comparisons.