TY - JOUR T1 - Classification of accelerometer wear and non-wear events in seconds for monitoring free-living physical activity JF - BMJ Open JO - BMJ Open DO - 10.1136/bmjopen-2014-007447 VL - 5 IS - 5 SP - e007447 AU - Shang-Ming Zhou AU - Rebecca A Hill AU - Kelly Morgan AU - Gareth Stratton AU - Mike B Gravenor AU - Gunnar Bijlsma AU - Sinead Brophy Y1 - 2015/05/01 UR - http://bmjopen.bmj.com/content/5/5/e007447.abstract N2 - Objective To classify wear and non-wear time of accelerometer data for accurately quantifying physical activity in public health or population level research.Design A bi-moving-window-based approach was used to combine acceleration and skin temperature data to identify wear and non-wear time events in triaxial accelerometer data that monitor physical activity.Setting Local residents in Swansea, Wales, UK.Participants 50 participants aged under 16 years (n=23) and over 17 years (n=27) were recruited in two phases: phase 1: design of the wear/non-wear algorithm (n=20) and phase 2: validation of the algorithm (n=30).Methods Participants wore a triaxial accelerometer (GeneActiv) against the skin surface on the wrist (adults) or ankle (children). Participants kept a diary to record the timings of wear and non-wear and were asked to ensure that events of wear/non-wear last for a minimum of 15 min.Results The overall sensitivity of the proposed method was 0.94 (95% CI 0.90 to 0.98) and specificity 0.91 (95% CI 0.88 to 0.94). It performed equally well for children compared with adults, and females compared with males. Using surface skin temperature data in combination with acceleration data significantly improved the classification of wear/non-wear time when compared with methods that used acceleration data only (p<0.01).Conclusions Using either accelerometer seismic information or temperature information alone is prone to considerable error. Combining both sources of data can give accurate estimates of non-wear periods thus giving better classification of sedentary behaviour. This method can be used in population studies of physical activity in free-living environments. ER -