Understanding of the Single-Item Physical Activity Question for Population Surveillance

BACKGROUND: Sport New Zealand conducts continuous representative "Active NZ" surveys. Between 2019 and 2020 (n = 13,887), these surveys asked International Physical Activity Questionnaire (IPAQ)-long-form questions, the single-item days (SI-days) per week question, and 1 question on hours per week (single-item hours [SI-hours] per week). This study examines relationships between the established SI-days question and meeting physical activity (PA) guidelines (150 min moderate-to-vigorous physical activity per week from SI-hours question and IPAQ). METHODS: Analyses were descriptive, and the best fit between SI-days and the PA thresholds was estimated using area under the receiver operator characteristic curves and Youden index. RESULTS: Using SI-hours, 60.6% achieved 150+ minutes; 85.2% reported the IPAQ-total minimum threshold, and 40.8% met the IPAQ-leisure time PA-only threshold. Receiver operator characteristic analyses showed area under the curve values with IPAQ between 0.63 and 0.76, but the SI-days showed a very good area under the curve of 0.82 (0.81-0.83) with the SI-hours 150-minute threshold. Youden index suggested the best fit was at 3+ days per week for maximizing Sensitivity and Specificity to meet IPAQ or SI-hours-defined PA guidelines. DISCUSSION: The SI-days per week question reflects achieving PA guidelines, and the best fit was with the SI-hours per week question. This provides surveillance-relevant concurrent validity for the SI-days measure, but the cut point for broadly meeting guidelines appears to be at least 3 days per week, not 5 days per week as previously thought.