Agreement between self-reported and accelerometer-measured physical activity in the Danish HBSC study

Objective: This cross-sectional study aims to assess the agreement between self-reported MVPA and VPA in leisure time, as reported in the international Health Behaviour in School-aged Children (HBSC) study, and device-based measures from accelerometers in a large national sample of Danish adolescents.
Methods: A total of 2400 adolescents (54% girls) aged 11-15 years wore accelerometers (Axivity AX3) to measure MVPA and VPA. They self-reported the number of days (0-7) they engaged in at least 60 minutes of physical activity per day. Compliance with physical activity guidelines was defined as 7 days of self-reported MVPA (of at least 60 minutes per day) and at least 60 minutes of MVPA per average day according to accelerometry. Cohen’s Kappa correlations were used to analyze the association between self-report and device-based measurements for the entire sample, as well as gender and age-stratified groups for meeting MVPA guidelines and VPA in leisure time.
Results: Survey data shows that 13% meet the recommendation of being physically active every day, while accelerometer data indicates that this applies to 32%. Thus, the survey method underestimates the proportion of those who adhere to the recommendations for physical activity. The study found low to fair correlations (0.16–0.30) between self-report and accelerometer MVPA across gender and age groups, with the lowest correlations among the youngest age group. The agreement between self-report and accelerometry data was good for specificity (91 %), but sensitivity was low (23 %), possibly due to poor compliance with recommendations.
Comparing self-reported and accelerometer-measured days with VPA in leisure time, showed fair to moderate correlations (0.29-0.49) across gender and age groups, with the highest correlation found for 15-year-olds.
Conclusions: The self-report questionnaire for MVPA and VPA demonstrates low to moderate validity compared to accelerometry, varying depending on the specific physical activity item and sex and age groups.