Darcy Ummels

The validation of a pocket worn activity tracker | 105 5 Discussion Principal findings This study showed that the optimized algorithm parameter settings (MOX MissActivity ) can more validly measure step count and physical behavior expressed as dynamic, standing, and sedentary time in older adults wearing an activity tracker in their trouser pocket during ADL based on a test combination of PE, APE, correlation coefficients, and paired sample t ‐ test compared to the MOX Annegarn , activPAL, and Fitbit. The variables step count and sedentary time showed good validity in comparison with the gold standard. It was hypothesised that all variables of the MOX MissActivity would have at least a substantial correlation ( r ≥0 .60) and an APE of < 10%. Only the variable dynamic time had a slightly lower correlation coefficient of 0.55 and the variables dynamic and standing time had a mean APE of 15.9% and 19.9%. These results are supported with additional analyzes of the specificity, sensitivity, and accuracy (Supplementary Table S5.2). This can be explained by the fact that the activities in the activity protocol were classified into dynamic, standing, and sedentary behavior as a whole. For example, by definition, the video observations classified changing linens as dynamic behavior, however during this activity it is possible that the participant performed a sequence of standing and dynamic behavior (e.g., standing still to put the cushion on the bed). In the current study, MOX Annegarn , activPAL, and Fitbit showed lower validity compared to the gold standard and the MOX MissActivity . It is clear that these target group and wear location specific classification algorithms cannot be applied outside of their specific context. The results for the activPAL are in line with a recent study showing a low validity during short stepping bouts and activities with low walking speeds, such as shuffling, picking, transitions, and kneeling in older adults. 40,41 The underestimation for dynamic time of the Fitbit can be explained by the definition Fitbit uses for active minutes: 10 continuous minutes long bouts of moderate ‐ to intense activity >3 MET. It is reasonable to assume that activities of daily living weren’t performed with such intensity and/or for that long during this protocol. Limitations and strengths This study had some limitations, the first one being the relatively low sample size ( n = 20). Future work could include a larger sample size, although several validity studies have been performed with a sample size of 20. 14 Second, that due to some technical errors, there were five missing values for both the Fitbit and the activPAL. However, since these activity trackers were only used as reference this should not have affected the main purpose of the current study. Third,