The primary aim was to validate questionnaire‐based insomnia diagnoses from a modified Karolinska Sleep Questionnaire (KSQ) and the Insomnia Severity Index (ISI), by age category (< or >65 years), against a semi‐structured face‐to‐face interview. Secondary aims were to split validity by diagnostic certainty of the interview and to compare prevalence estimates of questionnaire‐ and interview‐based diagnoses. A total of 232 out of 1,200 invited (19.3%) from the fourth Nord‐Trøndelag Health Study (HUNT4) completed questionnaires, including the KSQ and ISI, shortly before attending a face‐to‐face diagnostic interview for insomnia based on the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM‐5). Both a tentative (DSM‐5 criteria A–E) and a definite (criteria A–H) interview diagnosis was evaluated. Cohen’s kappa statistic quantified questionnaire validity. In all, 33% (95% confidence interval 27–39%) of participants had definite insomnia: 40% of women and 21% of men. The ISI (cut‐off 12) and several KSQ‐based diagnoses showed very good validity (κ ≤0.74) against the tentative, versus good validity (κ ≤0.61) against the definite interview diagnosis. Short questionnaires, requiring a daytime symptom at least three times a week, may underestimate insomnia prevalence. Validity was consistently higher for persons aged below versus above 65 years (definite insomnia: κ ≤0.64 vs. κ ≤0.56). Our results have implications for epidemiological population‐based studies utilising insomnia questionnaires.

Questionnaires for restless legs syndrome have rarely been validated against faceto-face interviews in the general population. We aimed to validate the modified Norwegian, seven-item Cambridge-Hopkins restless legs syndrome questionnaire and a single diagnostic question for restless legs syndrome. We also aimed to stratify validity at 65 years of age. Among a random sample of 1,201 participants from the fourth wave of the Trøndelag Health Study, 232 (19%) agreed to participate, out of whom 221 had complete data for analyses. Participants completed the questionnaires for restless legs syndrome immediately before attending a face-to-face interview using the latest diagnostic criteria. We calculated sensitivity, specificity, and Cohen's kappa statistic (κ) of questionnaire-versus interview-based diagnoses. We found acceptable validity of the seven-item modified Cambridge-Hopkins diagnostic questionnaire for restless legs syndrome (κ = 0.37, 95% confidence interval [CI] 0.23-0.51) and good validity of the single diagnostic question (κ = 0.47, 95% CI 0.35-0.58). We also found good validity through the combination of modified Cambridge-Hopkins diagnostic questionnaire for restless legs syndrome items 2 and 5, while item 1 or 2 alone showed only acceptable validity. The single diagnostic question was significantly more valid among those aged <65 years (κ = 0.60 versus κ = 0.26). Both singleand two-item questionnaire-based diagnoses overestimated interview-based restless legs syndrome prevalence. The seven-item modified Cambridge-Hopkins diagnostic questionnaire for restless legs syndrome will be useful for epidemiological studies although low sensitivity may cause underestimation of true restless legs syndrome prevalence in the general population, especially among elderly. Brief questionnairebased diagnoses of up to three items seem best utilised as an initial screen. Future studies should identify brief and even more valid questionnaire-based diagnoses for restless legs syndrome in order to estimate prevalence accurately in large epidemiological studies.