• C Tudor-Locke, L Burkett, J P Reis, B E Ainsworth, C A Macera, and D K Wilson.
• Department Exercise and Wellness, Arizona State University East, Mesa, AZ 85212, USA. Tudor-Locke@asu.edu
• Prev Med. 2005 Mar 1; 40 (3): 293-8.

BackgroundThe study purpose was to establish the number (and type) of days needed to estimate mean pedometer-determined steps/day in a field setting.MethodsSeven days of data were collected from 90 participants (33 males, age = 49.1 +/- 16.2 years, BMI = 27.2 +/- 4.1 kg/m(2); 57 females, age = 44.8 +/- 16.9 years, BMI = 27.0 +/- 5.9 kg/m(2)). Mean steps/day were computed for all 7 days (the criterion), each single day, and combinations of days. Analyses included repeated measures ANOVA, intra-class correlations (ICC), and regression.ResultsThere was a significant difference (P < 0.001) between days. The difference was limited to Sunday and accounted for 5% of the variance. ICC analyses indicated a minimum of 3 days is necessary to achieve a reliability of 0.80. The adjusted R(2) was 0.79 for a single day (specifically Wednesday), 0.89 for 2 days (Wednesday, Thursday), and 0.94 for 3 days (Wednesday, Thursday, Friday). Sunday was the last day to enter the model.ConclusionsAlthough there is a statistical difference between days, there is little practical difference, and the primary distinction appears limited to Sunday. Although a single day of collection is not acceptable, any 3 days can provide a sufficient estimate.

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