Evaluation of an instrument assessing influence of Gout on health-related quality of life

OBJECTIVE: To evaluate the reliability and validity of an instrument assessing the influence of gout (acute and chronic) on health-related quality of life (HRQOL). METHODS: Focus groups were used to examine the content of an existing Gout Assessment Questionnaire (GAQ1.0). GAQ2.0 was developed, consisting of a section describing the impact of gout on HRQOL [Gout Impact (GI)] and 4 sections describing subjects' gout overall and demographic data. The GAQ2.0 and the Medical Outcomes Study Short Form-36 Version 2 (SF-36v2) were completed by gout patients in 3 US cities. GI scales were examined using clinical judgment, review of item statistics, Rasch analysis, and confirmatory factor analysis. RESULTS: Subjects (n = 308) were predominantly male (90.2%), Caucasian (75.9%), with a mean age 62.2 +/- 11.8 years. Half the subjects (49.7%) reported > or = 3 attacks in the past year. Two-week test-retest reliability for each scale was good (0.77 to 0.89) for all 5 GI scales. All scales achieved high sufficient (0.86 to 0.89) or excellent (0.93 to 0.97) ratings based on 10-item adjusted alpha coefficients. Correlations and tests among known groups indicated subjects with more severe gout had higher GI scores (i.e., greater gout impact). GI scores correlated more highly with patient-reported measures of gout severity than the SF-36v2 and several traditional measures of gout severity. CONCLUSION: The GAQ2.0 is an instrument for measuring the impact of gout on HRQOL. The GI section exhibited acceptable reliability and validity characteristics. Future studies should assess GI responsiveness, minimally important differences, and psychometric properties in other patient populations.