Nonparticipation Bias in Accelerometer-Based Studies and the Use of Propensity Scores

Relatively little attention has been paid to the effects of nonparticipation on data quality in population-based studies that use accelerometers to measure physical activity. We examine these issues using data from the 2013 Longitudinal Internet Studies for the Social Sciences (LISS) panel and 2013-2014 National Health and Nutrition Examination Survey (NHANES) accelerometer studies, both of which collected survey data in advance and therefore permit comparisons of self-reported physical activity between participants and nonparticipants to the accelerometer studies. While individuals with high levels of self-reported physical activity are overrepresented in the participant samples, the differences are modest in both studies. However, in the LISS panel this difference led to overestimates of physical activity that are not fully corrected by propensity score weighting adjustments (i.e., non-ignorable selection bias). This finding underscores the importance of assessing the potential influence of nonparticipation on accelerometer-derived estimates of physical activity.