The standard gamble showed better construct validity than the time trade-off
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BACKGROUND AND OBJECTIVE: There is little evidence for the relative cross-sectional validity of the standard gamble (SG) and time trade-off (TTO). We compared these preference-based instruments in patients with Irritable Bowel Syndrome (IBS). METHODS: Patients rated their own health on the SG and TTO and completed the disease-specific IBS questionnaire, the Brief Pain Inventory, the SF-36, the Sickness Impact Profile, and a global rating of disease severity. RESULTS: Mean scores of the 96 enrolled patients (mean age 39.5 years, 84.4% women) were 0.84 (standard deviation 0.16) for the SG and 0.76 (0.22) for the TTO. The correlation of the SG with the TTO was 0.36. For the SG, correlation coefficients with the IBS questionnaire domain scores ranged from 0.36 to 0.47, whereas those of the TTO were substantially lower (0.15-0.42). The SG also had higher correlations than the TTO with generic questionnaires (0.18-0.34 versus 0.13-0.26), Brief Pain Inventory (0.27 versus 0.11), global rating of disease severity (0.22 versus 0.10) as well as with SF-36-derived patient preferences (0.31-0.43 versus 0.27-0.31). CONCLUSIONS: The higher correlations of the SG with validation measures indicate that the SG better reflects health-related quality of life and patient preferences compared to the TTO.
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