Accelerometer test-retest reliability by data processing algorithms: Results from the Twin cities walking study

John R. Sirard, Ann Forsyth, J. Michael Oakes, Kathryn H. Schmitz

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


Background: The purpose of this study was to determine 1) the test-retest reliability of adult accelerometermeasured physical activity, and 2) how data processing decisions affect physical activity levels and test-retest reliability. Methods: 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. Results: 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. Conclusions: 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.

Original languageEnglish (US)
Pages (from-to)668-674
Number of pages7
JournalJournal of Physical Activity and Health
Issue number5
StatePublished - Jul 2011


  • Accelerometry
  • Data processing
  • Physical activity assessment
  • Reliability


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