Evaluating Mailed Motivational, Individually Tailored Postcard Boosters for Promoting Girls' Postintervention Moderate-to-Vigorous Physical Activity.

The sample was small (181 girls from three schools), which limits generalizability. Schools were assigned to conditions, but analyses were done at the individual level, so girls in the same school may have been more similar than the analysis assumed. The groups were not identical at baseline: the no-booster intervention group had higher proportions of Hispanic girls and girls enrolled in free or reduced-price lunch programs than the booster and control groups. The study did not assess whether girls completed the activities on the postcards, only whether they received or read them. Girls' self-reports of becoming more active were not supported by accelerometer data, and the authors suggest favorable evaluations may reflect social acceptability bias.

Do not conclude the postcards increased girls' physical activity because many said they became more active. Accelerometer data showed no group difference, and activity decreased from baseline to 9 months.