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Reactivity is defined as a change in normal activity patterns when people are aware that their activity levels are being monitored. This study investigated reactivity in elementary school children. The step counts of forty-eight participants in second, fourth and sixth grades were monitored with sealed pedometers for eight days. A factorial repeated measures ANOVA revealed no significant differences among days for all participants ( F (7,294) = 1.25, p = .279) and no interactions among Sex, Grade, and Day. There is no reactivity in children monitored with a sealed pedometer. Intraclass correlations found that three to four days of monitoring are needed to determine habitual activity levels with a coefficient alpha level of .70 and five days of monitoring are needed to obtain a .80 coefficient alpha. This study demonstrates that there appears to be no reactivity period when sealed pedometers are used to measure physical activity.
Vincent et al. (2002) studied this question.