Increased use of the Internet over the past decade provides new opportunities to use Web-based questionnaires in epidemiological studies. Compared to traditional paper-based questionnaires, Web-based alternatives may simplify data collection and improve the quality of data [1-3]. The need to design and validate questionnaires specifically for use on the Web has, therefore, increased in recent years. Many Web-based questionnaires used today are directly transferred from printed questionnaires rather than being originally developed for the medium in which they are used. Thus, few take advantage of the potential interactive features offered by the Web. For example, the burden on the respondent can be decreased by using follow-up questions, and errors can be minimized by implementing automatic controls for missing, inconsistent, or anomalous answers [4].
At present, there are few physical activity questionnaires available specifically developed for the Web. To the best of our knowledge, only one Web-based questionnaire (that assessed lifetime physical activity) has been validated and showed acceptable results [5]. Therefore, we developed a series of interactive questionnaires that assess total physical activity and inactivity in different age groups. The Active-Q questionnaire assesses physical activity and inactivity during the past year in subjects over 18 years.
The primary aim of this study was to test the validity of Active-Q against the doubly labeled water (DLW) method, the criterion standard for measuring energy expenditure [6]. Furthermore, the reproducibility of Active-Q was assessed by comparing the results obtained from the questionnaire on two separate occasions.