title: Individual characteristics associated with mismatches between self-reported and accelerometer-measured physical activity.
abstract: BACKGROUND
  Accurate assessment tools are required for the surveillance of physical activity (PA) levels and the assessment of the effect of interventions. In addition, increasing awareness of PA is often used as the first step in pragmatic behavioural interventions, as discrepancies between the amount of activity an individual perceives they do and the amount actually undertaken may act as a barrier to change. Previous research has demonstrated differences in the amount of activity individuals report doing, compared to their level of physical activity when measured with an accelerometer. Understanding the characteristics of those whose PA level is ranked differently when measured with either self-report or accelerometry is important as it may inform the choice of instrument for future research. The aim of this project was to determine which individual characteristics are associated with differences between self-reported and accelerometer measured physical activity.
  
  
  METHODS
  Participant data from the 2009 wave of the Commuting and Health in Cambridge study were used. Quartiles of self-reported and accelerometer-measured PA were derived by ranking each measure from lowest to highest. These quartiles were compared to determine whether individuals' physical activity was ranked higher by either method. Multinomial logistic regression models were used to investigate the individual characteristics associated with different categories of mismatch.
  
  
  RESULTS
  Data from 486 participants (70% female) were included in the analysis. In adjusted analyses, the physical activity of overweight or obese individuals was significantly more likely to be ranked higher by self-report than by accelerometer than that of normal-weight individuals (OR = 2.07, 95%CI = 1.28-3.34), particularly among women (OR = 3.97, 95%CI = 2.11-7.47).
  
  
  CONCLUSIONS
  There was a greater likelihood of mismatch between self-reported and accelerometer measured physical activity levels in overweight or obese adults. Future studies in overweight or obese adults should consider employing both methods of measurement.
authors.affiliation: UKCRC Centre of Excellence for Public Health (NI), Centre for Public Health, Institute for Clinical Science (B), Royal Victoria Hospital, Belfast, United Kingdom.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Tully
authors.affiliation: MRC Epidemiology Unit and UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Cambridge Biomedical Campus, Cambridge, United Kingdom.
authors.forename: Jenna
authors.initials: J
authors.lastname: Panter
authors.affiliation: MRC Epidemiology Unit and UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Cambridge Biomedical Campus, Cambridge, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Ogilvie
mesh_terms: D061725:Accelerometry / Q000379:methods; D000328:Adult; D000368:Aged; D001364:Awareness; D002755:Choice Behavior / Q000502:physiology*; D005260:Female; D015438:Health Behavior; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity; D050177:Overweight; D057566:Self Report; D014186:Transportation / Q000379:methods; D055815:Young Adult