Figure 1.

Design of a validation study of the Oxford WebQ, an online 24-hour dietary questionnaire, United Kingdom, 2014–2016. Each 24-hour dietary assessment (the Oxford WebQ online tool and the interviewer-based multiple-pass 24-hour recall, in random order) and selected reference measurements (recovery biomarkers, predictive biomarkers, and total energy expenditure) were completed on 3 different occasions separated by approximately 2 weeks. On each occasion, the reference measurement was followed 1–3 days later by the first dietary assessment, which was followed approximately 2–4 days later by the second dietary assessment.