title: Validity of the global physical activity questionnaire (GPAQ) in assessing levels and change in moderate-vigorous physical activity and sedentary behaviour.
abstract: BACKGROUND
  Feasible, cost-effective instruments are required for the surveillance of moderate-to-vigorous physical activity (MVPA) and sedentary behaviour (SB) and to assess the effects of interventions. However, the evidence base for the validity and reliability of the World Health Organisation-endorsed Global Physical Activity Questionnaire (GPAQ) is limited. We aimed to assess the validity of the GPAQ, compared to accelerometer data in measuring and assessing change in MVPA and SB.
  
  
  METHODS
  Participants (n = 101) were selected randomly from an on-going research study, stratified by level of physical activity (low, moderate or highly active, based on the GPAQ) and sex. Participants wore an accelerometer (Actigraph GT3X) for seven days and completed a GPAQ on Day 7. This protocol was repeated for a random sub-sample at a second time point, 3-6 months later. Analysis involved Wilcoxon-signed rank tests for differences in measures, Bland-Altman analysis for the agreement between measures for median MVPA and SB mins/day, and Spearman's rho coefficient for criterion validity and extent of change.
  
  
  RESULTS
  95 participants completed baseline measurements (44 females, 51 males; mean age 44 years, (SD 14); measurements of change were calculated for 41 (21 females, 20 males; mean age 46 years, (SD 14). There was moderate agreement between GPAQ and accelerometer for MVPA mins/day (r = 0.48) and poor agreement for SB (r = 0.19). The absolute mean difference (self-report minus accelerometer) for MVPA was -0.8 mins/day and 348.7 mins/day for SB; and negative bias was found to exist, with those people who were more physically active over-reporting their level of MVPA: those who were more sedentary were less likely to under-report their level of SB. Results for agreement in change over time showed moderate correlation (r = 0.52, p = 0.12) for MVPA and poor correlation for SB (r = -0.024, p = 0.916).
  
  
  CONCLUSIONS
  Levels of agreement with objective measurements indicate the GPAQ is a valid measure of MVPA and change in MVPA but is a less valid measure of current levels and change in SB. Thus, GPAQ appears to be an appropriate measure for assessing the effectiveness of interventions to promote MVPA.
authors.forename: Claire L
authors.initials: CL
authors.lastname: Cleland
authors.forename: Ruth F
authors.initials: RF
authors.lastname: Hunter
authors.forename: Frank
authors.initials: F
authors.lastname: Kee
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Cupples
authors.forename: James F
authors.initials: JF
authors.lastname: Sallis
authors.affiliation: UKCRC Centre of Excellence for Public Health (NI), Centre for Public Health, School of Dentistry, Medicine and Biomedical Sciences, Queen's University Belfast, Clinical Sciences Block B, Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BJ, Northern Ireland. m.tully@qub.ac.uk.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Tully
mesh_terms: D061725:Accelerometry; D000328:Adult; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009660:Northern Ireland / Q000453:epidemiology; D015203:Reproducibility of Results; D057185:Sedentary Behavior; D057566:Self Report; D011795:Surveys and Questionnaires / Q000592:standards*; D013997:Time Factors; D014944:World Health Organization