title: Validity and repeatability of a simple index derived from the short physical activity questionnaire used in the European Prospective Investigation into Cancer and Nutrition (EPIC) study.
abstract: OBJECTIVE
  To assess the validity and repeatability of a simple index designed to rank participants according to their energy expenditure estimated by self-report, by comparison with objectively measured energy expenditure assessed by heart-rate monitoring with individual calibration.
  
  
  METHODS
  Energy expenditure was assessed over one year by four separate episodes of 4-day heart-rate monitoring, a method previously validated against whole-body calorimetry and doubly labelled water. Cardio-respiratory fitness was assessed by four repeated measures of sub-maximum oxygen uptake. At the end of the 12-month period, participants completed a physical activity questionnaire that assessed past-year activity. A simple four-level physical activity index was derived by combining occupational physical activity together with time participating in cycling and other physical exercise (such as keep fit, aerobics, swimming and jogging).
  
  
  METHODS
  One hundred and seventy-three randomly selected men and women aged 40 to 65 years.
  
  
  RESULTS
  The repeatability of the physical activity index was high (weighted kappa=0.6, ). There were positive associations between the physical activity index from the questionnaire and the objective measures of the ratio of daytime energy expenditure to resting metabolic rate and cardio-respiratory fitness As an indirect test of validity, there was a positive association between the physical activity index and the ratio of energy intake, assessed by 7-day food diaries, to predicted basal metabolic rate.
  
  
  CONCLUSIONS
  The summary index of physical activity derived from the questions used in the European Prospective Investigation into Cancer and Nutrition (EPIC) study suggest it is useful for ranking participants in terms of their physical activity in large epidemiological studies. The index is simple and easy to comprehend, which may make it suitable for situations that require a concise, global index of activity.
authors.affiliation: Department of Public Health and Primary Care, Institute of Public Health, University of Cambridge, Robinson Way, CB2 2SR, UK. njw1004@medschl.cam.ac.uk
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Wareham
authors.forename: Rupert W
authors.initials: RW
authors.lastname: Jakes
authors.forename: Kirsten L
authors.initials: KL
authors.lastname: Rennie
authors.forename: Jantine
authors.initials: J
authors.lastname: Schuit
authors.forename: Jo
authors.initials: J
authors.lastname: Mitchell
authors.forename: Susie
authors.initials: S
authors.lastname: Hennings
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Day
mesh_terms: D000328:Adult; D000368:Aged; D001481:Basal Metabolism; D015331:Cohort Studies; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007899:Leisure Activities; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010809:Physical Fitness; D011446:Prospective Studies; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity