title: Validity and reproducibility of a physical activity questionnaire for older adults: questionnaire versus accelerometer for assessing physical activity in older adults.
abstract: BACKGROUND
  Physical activity (PA) is important in older adults for the maintenance of functional ability. Assessing PA may be difficult. Few PA questionnaires have been compared to activity monitors. We examined reproducibility and validity of the self-administered Longitudinal Ageing Study Amsterdam Physical Activity Questionnaire (LAPAQ) against a triaxial accelerometer (ACTR) (Sensewear(®) Pro) in older adults.
  
  
  METHODS
  Participants wore the ACTR continuously for two weeks. After 2 (T [time] = 1) and 4 (T = 2) weeks, participants completed the LAPAQ. Since the LAPAQ asks about 2 weeks' worth of physical activity, the ACTR and LAPAQ coincided at T1. T2 was used to assess the reproducibility of the LAPAQ results only. We calculated Pearson's correlation coefficients (PCC) to examine reproducibility and validity. For visualization, we used scatterplots and Bland-Altman plots. With a receiver operating characteristics (ROC) curve we assessed how well the LAPAQ identifies older adults whose activity level is below official recommendations.
  
  
  RESULTS
  A total of 89 persons were included. Of the participants, 48% were men; median age was 73, and median body mass index was 25. The 2-week mean total duration of activity was 2788 (ACTR, T = 1), 2439 (LAPAQ T = 1), and 1994 (LAPAQ T = 2) minutes. As a reference, 2 full weeks contained 20,160 minutes. Reproducibility of the LAPAQ was moderate (PCC 0.68, 95% CI 0.55-0.80). The median difference between LAPAQ at T = 1 and the ACTR (LAPAQ minus ACTR) was -510 minutes and the PCC was 0.25 (95% CI 0.07-0.44). The area under the ROC curve was 0.73 (95% CI 0.59-0.86).
  
  
  CONCLUSIONS
  LAPAQ underestimates PA and seems unsuitable for exact measurement in older adults. However, it may be used to determine if a person's PA level is below the recommended level.
authors.affiliation: Department of General Practice, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Lara
authors.initials: L
authors.lastname: Siebeling
authors.forename: Sarah
authors.initials: S
authors.lastname: Wiebers
authors.forename: Leo
authors.initials: L
authors.lastname: Beem
authors.forename: Milo A
authors.initials: MA
authors.lastname: Puhan
authors.forename: Gerben
authors.initials: G
authors.lastname: Ter Riet