Evaluating the feasibility of measuring travel to school using a wearable camera

Background: The school journey is often studied in relation to health outcomes in children and adolescents. Self-report is the most common measurement tool. Purpose: To investigate the error on self-reported journey duration in adolescents, using a wearable digital camera (Microsoft SenseCam). Methods: During March-May 2011, participants (n=17; aged 13-15 years) from four schools wore wearable cameras to and from school for 1 week. The device automatically records time-stamped, first-person point-of-view images, without any action from the wearer. Participants also completed a researcher-administered self-report travel survey over the same period. Analysis took place in November 2011. Within- and between-subjects correlation coefficients and Bland-Altman 95% limits of agreement were derived, accounting for the multiple observations per individual. Results: Self-report data were collected for 150 journey stages and SenseCam data for 135 (90%) of these. The within-subjects correlation coefficient for journey duration was 0.89 (95% CI=0.84, 0.93). The between-subjects correlation coefficient was 0.92 (95% CI=0.79, 0.97). The mean difference (bias) between methods at the whole sample level was small (10 seconds per journey, 95% CI= -33, 53). The wide limits of agreement (±501 seconds, 95% CI= -491, 511) reveal large random error. Conclusions: Compared to direct observation from images, self-reported journey duration is accurate at the mean group level but imprecise at the level of the individual participant.