Use of the short form of King's Health Questionnaire to measure quality of life in patients with an overactive bladder.

OBJECTIVE: To develop a short version of the King's Health Questionnaire (KHQ), as there is a practical need to have a shorter version to summarize the eight domain scores into fewer domains.

PATIENTS AND METHODS: Data from 293 patients were obtained from a randomized, double-blind, placebo-controlled clinical trial in Japan of oxybutynin and tolterodine in patients with symptoms of an overactive bladder. The KHQ has two single-item and six multiple-item domains. To construct the short form of the KHQ one item was selected from the each of multiple-item domains, based on standardized structural coefficients estimated by confirmatory factor analysis (CFA) in a previous study. These six items include the domains: 'daily activities from role limitation', 'travel from physical limitation', 'social life from social limitation', 'family life from personal relationship', 'depressed from emotion' and 'tired from sleep and energy'. Based on the six selected items a series of psychometric analyses were conducted.

RESULTS: Exploratory factor analysis (EFA) with promax rotation identified two factors 'limitation of daily life' (LDL) and mental health. LDL consisted of 'daily activities', 'travel' and 'social life', and mental health included 'family life', 'depressed' and 'tired'. Based on the results from the EFA, the second-order factor structure was tested by CFA. The model fitted the data well for both the male and female model. The KHQ short form showed excellent reliability with Cronbach's alpha coefficients for LDL and mental health for both genders. The domains in the short form were responsive to clinical efficacy variables, and had statistically significant sensitivity to change in the patients' perception of bladder condition in all domains.

CONCLUSION: These analyses confirm the psychometric properties and clinical validity of the short-form KHQ, which appears to offer a practical, valid and reliable health-related quality-of-life instrument.