How many days of pedometer monitoring predict weekly physical activity in adults?

Prev Med. 2005 Mar;40(3):293-8. doi: 10.1016/j.ypmed.2004.06.003.


Background: The study purpose was to establish the number (and type) of days needed to estimate mean pedometer-determined steps/day in a field setting.

Methods: Seven 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.

Results: There 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.

Conclusions: Although 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.

Publication types

  • Clinical Trial
  • Research Support, U.S. Gov't, P.H.S.
  • Validation Study

MeSH terms

  • Adult
  • Female
  • Humans
  • Male
  • Middle Aged
  • Monitoring, Physiologic / instrumentation
  • Monitoring, Physiologic / methods*
  • Monitoring, Physiologic / standards*
  • Motor Activity / physiology*
  • Predictive Value of Tests
  • Reference Standards
  • Regression Analysis
  • Reproducibility of Results
  • Time Factors
  • Walking / physiology*