Test-retest reliability of a computer-assisted self-administered questionnaire on early life exposure in a nasopharyngeal carcinoma case-control study

We evaluated the reliability of early life nasopharyngeal carcinoma (NPC) aetiology factors in the questionnaire of an NPC case-control study in Hong Kong during 2014–2017. 140 subjects aged 18+ completed the same computer-assisted questionnaire twice, separated by at least 2 weeks. The questionnaire included most known NPC aetiology factors and the present analysis focused on early life exposure. Test-retest reliability of all the 285 questionnaire items was assessed in all subjects and in 5 subgroups defined by cases/controls, sex, time between 1 st and 2 nd questionnaire (2–29/≥30 weeks), education (secondary or less/postsecondary), and age (25–44/45–59/60+ years) at the first questionnaire. The reliability of items on dietary habits, body figure, skin tone and sun exposure in early life periods (age 6–12 and 13–18) was moderate-to-almost perfect, and most other items had fair-to-substantial reliability in all life periods (age 6–12, 13–18 and 19–30, and 10 years ago). Differences in reliability by strata of the 5 subgroups were only observed in a few items. This study is the first to report the reliability of an NPC questionnaire, and make the questionnaire available online. Overall, our questionnaire had acceptable reliability, suggesting that previous NPC study results on the same risk factors would have similar reliability.