Objectives: To develop and assess the psychometric properties of a short self-report nocturia-specific Quality-of-Life (QOL) questionnaire.
Methods: The Nocturia Quality-of-Life questionnaire (N-QOL) was developed using focus group interviews with men experiencing nocturia. To refine it further and psychometrically validate the questionnaire, 107 men with nocturia (from four urology clinics in the United Kingdom) completed the pilot N-QOL, along with measures of health status and sleep quality. To assess reproducibility, men from one clinic completed the pilot N-QOL again at 1 week.
Results: After standard item reduction analyses, 18 items were dropped from the pilot questionnaire. The psychometric properties of the remaining 13-item instrument were tested in accordance with standard criteria. Factor analysis identified two subscales, sleep/energy and bother/concern, loading at 0.5 and greater. The N-QOL overall score and subscales proved to be internally consistent (alpha = 0.84 to 0.90) and reproducible (intraclass correlation coefficient = 0.74 to 0.82). N-QOL scores correlated with sleep quality (P <0.01) as measured by the Pittsburgh Sleep Quality Index and energy/vitality and social functioning (P <0.01) as measured by the SF-36 Health Survey, demonstrating good convergent validity. The N-QOL also demonstrated statistically significant differences between the scores of those experiencing one, two, and three or more episodes of nocturia on an average night, indicating excellent discriminant validity.
Conclusions: These analyses provide support for the psychometric validity of the N-QOL for use in a male population with nocturia.