A Priori Power Analysis
Our power calculations were based on similar studies reported in the literature [60–63] and
on results from a previous pilot study [29]. From these sources, effect sizes were observed in
the small to large range (Cohen’s d of 28–1.03) and we noted that the small effect sizes were
for non-central outcome measures (e.g., VO2 max. which had a median effect size of .39).
For variables that are similar to our primary outcomes (e.g., physical activity, activity
adherence), the median effect size was relatively large (d=.69). Given the several design
features of our study, such as regular contacts, no wait-list control to delay intervention
participation, monetary incentives, and overall validity improvements of the measures, we
anticipate that the effect sizes obtained for the intervention will be at least as large as these
rough estimates.