Mapping of the OAB-SF Questionnaire onto EQ-5D in Spanish Patients with Overactive Bladder

Mapping disease-specific measures onto generic preference-based indexes allows estimating utility values in specific conditions to determine gain of quality-adjusted-life-years when the status of condition varies. The aim of this study was to map a disease specific scale, the Overactive Bladder Questionnaire 5-dimensional health classification system (OAB-5D) derived from the Overactive Bladder questionnaire-Short Form (OABq-SF), onto a preference-based scale, the EuroQol-5D (EQ-5D), in a sample of patients with overactive bladder (OAB) in a Spanish population.

A survey addressed to value the health states was conducted among 246 patients at 18 clinics of urology from Spain. A total of 43 out of 243 possible health states have been valued, using VAS (Visual Analog Scale) and TTO (time trade-off) techniques. In addition, ordinary least squares (OLS), generalized linear models (GLM) and Tobit models were estimated. Resulting models were compared and the best one was selected in terms of goodness of fit measures, attribute sign, coefficient magnitude, and statistical significance of regression coefficients. Finally, the internal validity of the best model was calculated by bootstrap resampling.

The best model to map the OAB-5D onto EQ-5D could be estimated and the stability of parameter estimations was proved. The mentioned model estimated through OLS regression attained R (2) value of 0.892, with the aggregated data; with GLM (efficient maximum likelihood regression), Pearson χ (2) of 15.3 has been obtained; AIC (Akaike information criterion) = -550.9 and BIC (Bayesian information criterion) = -475.4. OLS model included the following OABq-SF items (and range of weights): A1 (0.102, 0.216); A3 (0.070, 0.171); B3 (0.071, 0.078); B1 (0.076, 0.136); B2 (-0.132, -0.028).

It is possible to map the OAB-5D scores onto EQ-5D in the Spanish population, allowing estimating EQ-5D utility scores from OAB specific health conditions.