Objective: There is a need for a measure of physical activity that assesses low, basic and high-intensity activities suitable for use in ageing research including falls prevention trials. We aimed to perform a formal validation of the Incidental and Planned Activity Questionnaire (IPAQ) by investigating its overall structure and measurement properties.
Design: Cross-sectional survey.
Setting: Community sample.
Participants: 500 older people (mean age: 77.4 years, SD: 6.08).
Main outcome measures: The IPAQ was administered as part of a longer assessment in two different postal self-completion formats; one for estimating physical activity during the last week (IPAQ-W) and one for estimating average weekly physical activity over the past three months (IPAQ-WA). Test–retest reliability was assessed by re-administration of the instruments one week later in a sub-sample of 80 respondents.
Results: Both IPAQ versions had good measurement properties, but overall the IPAQ-WA performed better than the IPAQ-W. Rasch analyses indicated the IPAQ-WA had an excellent overall fit. Analysis of the internal structure supported the unidimensionality of the scale with an acceptable internal consistency. The content representation of the items revealed three categories (low, moderate and high levels of physical activity), with a good contribution of items by threshold. The IPAQ-WA had excellent test–retest reliability, ICC=0.87) and was able to discriminate differences in physical activity levels between groups differentiated by sex, age, and fall risk factors.
Conclusions: the IPAQ has excellent psychometric properties and assesses the level of physical activity relating to both basic and more demanding activities. Further research is required to confirm sensitivity to change.