Accelerometer test-retest reliability by data processing algorithms: results from the Twin Cities Walking Study

• Published in: Journal of physical activity & health Vol. 8; no. 5; p. 668
• Main Authors: Sirard, John R, Forsyth, Ann, Oakes, J Michael, Schmitz, Kathryn H
• Format: Journal Article
• Language: English
• Published: United States 01.07.2011
• Subjects: Adult; Algorithms; Automatic Data Processing; Body Mass Index; Data Collection - instrumentation; Data Collection - methods; Exercise; Female; Humans; Male; Middle Aged; Minnesota; Reproducibility of Results; Residence Characteristics; Socioeconomic Factors; Minnesota
• ISSN: 1543-5474
• DOI: 10.1123/jpah.8.5.668

The purpose of this study was to determine 1) the test-retest reliability of adult accelerometer-measured physical activity, and 2) how data processing decisions affect physical activity levels and test-retest reliability. 143 people wore the ActiGraph accelerometer for 2 7-day periods, 1 to 4 weeks apart. Five algorithms, varying nonwear criteria (20 vs. 60 min of 0 counts) and minimum wear requirements (6 vs. 10 hrs/day for ≥ 4 days) and a separate algorithm requiring ≥ 3 counts per min and ≥ 2 hours per day, were used to process the accelerometer data. Processing the accelerometer data with different algorithms resulted in different levels of counts per day, sedentary, and moderate-to-vigorous physical activity. Reliability correlations were very good to excellent (ICC = 0.70-0.90) for almost all algorithms and there were no significant differences between physical activity measures at Time 1 and Time 2. This paper presents the first assessment of test-retest reliability of the Actigraph over separate administrations in free-living subjects. The ActiGraph was highly reliable in measuring activity over a 7-day period in natural settings but data were sensitive to the algorithms used to process them.