Can the standard gamble and rating scale be used to measure quality of life in rhinoconjunctivitis? Comparison with the RQLQ and SF-36
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BACKGROUND: With interest in health economics growing, it is important to know whether utilities may be used to measure health-related quality of life in patients with rhinoconjunctivitis. The objective was to compare the validity and measurement properties of disease-specific versions of the standard gamble and rating scale with those of the Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) and the Short-Form 36 (SF-36). METHODS: One hundred adults with symptomatic rhinoconjunctivitis participated in a 5 week observational study, completing the standard gamble, rating scale, RQLQ and SF-36 at baseline and after 1 and 5 weeks. Symptom diaries were completed for 1 week before each follow-up visit. RESULTS: Reliability was highest for the RQLQ (intraclass correlation coefficient = 0.97), followed by the rating scale (0.75), the SF-36 physical (0.75), the SF-36 mental (0.74) and the standard gamble (0.12). The responsiveness index was highest for the RQLQ (0.76), followed by the rating scale (0.56) and the SF-36 mental (0.28). Both cross-sectional and longitudinal validity were strongest for the RQLQ and the rating scale. CONCLUSIONS: Both the rating scale and the RQLQ have strong evaluative and discriminative properties. The SF-36 has acceptable discriminative properties but its evaluative properties are poor. All measurement properties for the standard gamble are inadequate. Poor correlation between the standard gamble and the rating scale indicates that utilities cannot be derived from rating scale data.
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