Comparisons of Accelerometer and Pedometer Determined Steps in Free Living Samples

Background: The purpose of this study was to compare steps.d(-1) between an accelerometer and pedometer in 2 free-living samples. Methods: Data from 2 separate studies were used for this secondary analysis (Sample 1 : N = 99, Male: n = 28, 20.9 +/- 1.4 yrs, BMI = 27.2 +/- 5.0 kg.m(-2), Female: n = 71, 20.9 +/- 1.7 yrs, BMI = 22.7 +/- 3.0 kg.m(-2); Sample 2 : N = 74, Male: n = 27, 38.0 +/- 9.5 yrs, BMI = 25.7 +/- 4.5 kg.m(-2), Female: n = 47, 38.7 +/- 10.1 yrs, BMI = 24.6 +/- 4.0 kg.m(-2)). Both studies used identical procedures and analytical strategies. Results: The mean difference in steps.d(-1) for the week was 1643.4 steps.d(-1) in Study 1 and 2199.4 steps.d(-1) in Study 2. There were strong correlations between accelerometer- and pedometer-determined steps.d(-1) in Study 1 (r = .85, P < .01) and Study 2 (r = 0.87, P < .01). Bland-Altman plots indicated agreement without bias between steps recorded from the devices in Study 1 (r = -0.14, P < .17) and Study 2 (r = -0.09, P < .40). Correlations examining the difference between accelerometer pedometer steps.d(-1) and MVPA resulted in small, inverse correlations (range: r = -0.03 to -0.28). Conclusions: These results indicate agreement between accelerometer- and pedometer-determined steps.d(-1); however, measurement bias may still exist because of known sensitivity thresholds between devices.