Equivalence of activity outcomes derived from three research grade accelerometers worn simultaneously on each wrist

This study evaluated the equivalence of activity outcomes from three accelerometer brands worn on both wrists during free living. Forty-four adults wore a GENEActiv, ActiGraph and Axivity accelerometer for 7 days. Outcomes were assessed between and within accelerometer brand and wrist location with average acceleration and the intensity gradient (IG) being of particular interest. Pairwise 95% equivalence tests and intra-class correlation coefficients (ICC) evaluated agreement. Average acceleration and the IG were largely equivalent between combinations of accelerometer device and wrists when applying a 10% equivalence zone. There was largely a lack of equivalence between pairings for time spent in acceleration values >= 100 mg. However, equivalence was largely achieved when applying an equivalence zone that encompassed values ranging from 0.3 to 0.45 SDs for IG and time spent above 100 mg and 150 mg. Agreement between pairings tended to be stronger between different brands on the non-dominant (ICCs >= 0.73-0.97) versus the dominant wrist (ICCs >= 0.57-0.97) and between wrists for the same accelerometer (ICCs >= 0.59-0.97) for average acceleration and the IG. These are important findings since device placement is not consistent in studies. Further work that applies an equivalence zone reflecting the variability of the outcome measure is encouraged.