Reliability and validity testing of a single-item physical activity measure

Objective To develop and test a new single-item physical activity screening tool, suitable for assessing respondents' eligibility for behaviour change interventions. Design Two single-item assessment tools were developed, one using a "past week" recall period, the other using a "past month" recall period. A quota sampling system was used to recruit 480 adults from across England, Scotland and Wales. Half the sample completed the past-week question and half completed the past-month version. Test-retest reliability was assessed over a 2- to 5-day period. Concurrent validity was assessed using the Global Physical Activity Questionnaire and the UK Active People Survey. All surveys were completed via telephone interviews. Results Both versions of the single-item instrument demonstrated strong reproducibility (r=0.72-0.82), using Spearman's rank correlation coefficients. The past-week recall question showed strong agreement in the classification of respondents meeting the current physical activity recommendation (kappa=0.63, 95% CI 0.54 to 0.72). Concurrent validity over the past week compared to the Global Physical Activity Questionnaire was modest (r=0.53) and slightly weaker for the past month compared to the Active People Survey (r=0.33-0.48). Conclusion Both versions of the new single-item measure performed as well as other short physical activity tools in terms of reliability and concurrent validity. Criterion validity testing of the single-item measure is recommended to establish its ability to assess objectively measured physical activity levels. In addition, further research to assess the responsiveness of the single-item measure in detecting changes in physical activity will inform its usefulness in programme evaluation.