Validity of two self-report measures of sitting time.

BACKGROUND In light of evidence linking sedentary behaviors to health outcomes, there have been calls for the measurement of sedentary behavior in surveillance studies. This study examined the convergent validity of 2 self-report measures of sitting time and accelerometer-determined sedentary time (minutes/day of <100 counts/minute). METHODS 44 adults wore an ActiGraph accelerometer for 7 days, during which they also recorded daily sitting time in a diary, in response to a single-item question. After 7 days, participants completed a new domain-specific questionnaire to assess usual weekday and weekend-day sitting time. Total sitting times recorded from the self-report measures were compared with accelerometer-determined sedentary time. RESULTS Total sitting time calculated from the domain-specific questionnaire did not differ significantly from accelerometer-determined sedentary time on weekdays (mean difference [±SE] = -14 ± 28 mins/day) and weekend days (-4 ± 45 mins/day, both P > .05). Sitting time was significantly underestimated using the single-item specific-day question on weekdays (-173 ± 18 mins/day) and weekend days (-219 ± 23 mins/day, both P < .001). CONCLUSIONS When assessed via self-report, the estimation of total sitting time is improved by summing sitting times reported across different domains. The continued improvement of self-report measures of sitting time will be important if we are to further our understanding of the links between sedentary behavior and health.