title: A Validation Study of the Web-Based Physical Activity Questionnaire Active-Q Against the GENEA Accelerometer.
abstract: BACKGROUND
  Valid physical activity assessment in epidemiological studies is essential to study associations with various health outcomes.
  
  
  OBJECTIVE
  To validate the Web-based physical activity questionnaire Active-Q by comparing results of time spent at different physical activity levels with results from the GENEA accelerometer and to assess the reproducibility of Active-Q by comparing two admissions of the questionnaire.
  
  
  METHODS
  A total of 148 men (aged 33 to 86 years) responded to Active-Q twice and wore the accelerometer during seven consecutive days on two occasions. Time spent on six different physical activity levels including sedentary, light (LPA), moderate (MPA), and vigorous (VPA) as well as additional combined categories of sedentary-to-light and moderate-to-vigorous (MVPA) physical activity was assessed. Validity of Active-Q was determined using Spearman correlation coefficients with 95% confidence intervals (CI) and the Bland-Altman method. Reproducibility was assessed using intraclass correlation coefficients (ICCs) comparing two admissions of the questionnaire.
  
  
  RESULTS
  The validity correlation coefficients were statistically significant for time spent at all activity levels; sedentary (r=0.19, 95% CI: 0.04-0.34), LPA (r=0.15, 95% CI: 0.00-0.31), sedentary-to-light (r=0.35, 95% CI: 0.19-0.51), MPA (r=0.27, 95% CI: 0.12-0.42), VPA (r=0.54, 95% CI: 0.42-0.67), and MVPA (r=0.35, 95% CI: 0.21-0.48). The Bland-Altman plots showed a negative mean difference for time in LPA and positive mean differences for time spent in MPA, VPA and MVPA. The ICCs of test-retest reliability ranged between r=0.51-0.80 for the different activity levels in Active-Q.
  
  
  CONCLUSIONS
  More moderate and vigorous activities and less light activities were reported in Active-Q compared to accelerometer measurements. Active-Q shows comparable validity and reproducibility to other physical activity questionnaires used today.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. stephanie.bonn@ki.se.
authors.forename: Stephanie Erika
authors.identifier: http://orcid.org/0000-0002-2219-7970
authors.initials: SE
authors.lastname: Bonn
authors.forename: Patrick
authors.identifier: http://orcid.org/0000-0003-4934-8684
authors.initials: P
authors.lastname: Bergman
authors.forename: Ylva
authors.identifier: http://orcid.org/0000-0001-6816-7577
authors.initials: Y
authors.lastname: Trolle Lagerros
authors.forename: Arvid
authors.identifier: http://orcid.org/0000-0001-5226-6685
authors.initials: A
authors.lastname: Sjölander
authors.forename: Katarina
authors.identifier: http://orcid.org/0000-0003-2046-5641
authors.initials: K
authors.lastname: Bälter
keywords: Internet; accelerometer; activity assessment; epidemiology; self report; validity