title: How many days of pedometer monitoring predict weekly physical activity in adults?
abstract: 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.
authors.affiliation: Department Exercise and Wellness, Arizona State University East, Mesa, AZ 85212, USA. Tudor-Locke@asu.edu
authors.forename: C
authors.initials: C
authors.lastname: Tudor-Locke
authors.forename: L
authors.initials: L
authors.lastname: Burkett
authors.forename: J P
authors.initials: JP
authors.lastname: Reis
authors.forename: B E
authors.initials: BE
authors.lastname: Ainsworth
authors.forename: C A
authors.initials: CA
authors.lastname: Macera
authors.forename: D K
authors.initials: DK
authors.lastname: Wilson
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods* / Q000592:standards*; D009043:Motor Activity / Q000502:physiology*; D011237:Predictive Value of Tests; D012015:Reference Standards; D012044:Regression Analysis; D015203:Reproducibility of Results; D013997:Time Factors; D016138:Walking / Q000502:physiology*