Background: Using self-reported surveys to monitor physical activity levels in the population require short items covering both time and intensity. The present study aims to 1) develop the Nordic Physical Activity Questionnaire-short from the original version of the NPAQ, 2) assess test-retest reliability and criterion validity of the NPAQ-short, and 3) test the NPAQ-short's ability to monitor compliance with the WHO recommendations on physical activity. In addition, we aimed to compare open and closed-ended answering modes for the NPAQ-short.
Methods: A sample of 122 participants were included. The NPAQ-short comprised of two questions on weekly moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA). It was filled in twice, two weeks apart, in open- and closed-ended versions. Physical activity was measured objectively by an Actiheart accelerometer worn 24 h/day seven consecutive days. Spearman's rank correlation and Cohen's kappa were used to assess correlations between the test and retest results, and between the objective and the self-reported measures.
Results: Valid data was available for 92 participants. Test-retest reliability showed Spearman's rho = 0.82 for MVPA and 0.80 for VPA. For the open-ended questions, the correlations between self-reported and objectively measured physical activity levels were Spearman's rho = 0.33 for MVPA and rho = 0.32 for VPA. For closed-ended questions, the kappa-coefficients were 0.17 for MVPA and 0.21 for VPA. When using objective and self-reported measures to monitor WHO's physical activity recommendations, the kappa correlations were 0.42 for open-ended and 0.34 for closed-ended answering modes.
Conclusion: The NPAQ-short was found to be sufficiently reliable and valid to monitor physical activity levels in the population when using both open and closed-ended questions. However, using open-ended questions seems to be a better answering mode for self-reported surveys monitoring WHO's physical activity recommendations.
Keywords: Actiheart; Closed-ended questions; NPAQ; Open-ended questions; Population survey; Self-administrated.