SUITABILITY OF CLAD-CQR MODELS FOR OBTAINING QALYS
Author(s)
Cunillera O1, Vilagut G1, Medina A2, Tresserra R2, Alonso J1, Brugulat P2, García C1, Ferrer M31IMIM (Institut de Recerca Hospital del Mar), Barcelona, Catalunya, Spain, 2Departament de Salut de la Generalitat de Catalunya, Barcelona, Catalunya, Spain, 3I
OBJECTIVES: The EQ-5D is the most used questionnaire to obtain utilities. Because of its index ceiling effect, Tobit and CLAD-CQR (Censored Least Absolute Deviations – Censored Quantile Regression) models are often used instead of Ordinal Least Squares for its modelization. CLAD models are usually presented as a robust alternative to the Tobit misspecification problems in presence of heteroskedasticity. The aim of this study is to evaluate the suitability of the CLAD-CQR models for the estimation of utilities and QALYs (Quality-Adjusted Life Years), to evaluate the impact of different chronic conditions in Catalan population’s health. METHODS: The EQ-5D was interview-administered in the 2006 Catalan Health Interview Survey, a cross-sectional study of a representative sample of the non-institutionalised general population (n=15,926). As well as CLAD-CQR, Tobit model was adjusted to assess utility losses associated with 15 chronic conditions. Goodness of fit was assessed by cross-validation (Mean Square Error –MSE-, Mean Absolute Deviations –MAD-). RESULTS: As ceiling effect was over 50%, CQR models on the 30 percentile had to be applied instead of CLAD models on the median. CQR showed a slightly worse fit to data (MSE=0.084, MAD=0.246) than Tobit (MSE=0.068, MAD=0.218). The impact of the different chronic conditions measured in QALYs obtained from the CQR was on average around 70% larger than the ones of the Tobit model. CONCLUSIONS: Tobit and CLAD-CQR model latent quality of life, not anchored in 0=death and 1=perfect health. While Tobit allows an estimation of observed utilities and marginal effects, interpretable as QALYs, CQR do not in the case of right-censoring. This leads to overestimation of effects and makes CLAD-CQR models inappropriate for obtaining QALYs, just as the untransformed Tobit’s latent variable. Moreover, the suitability of modelling percentiles differing from the median should be discussed.
Conference/Value in Health Info
2011-11, ISPOR Europe 2011, Madrid, Spain
Value in Health, Vol. 14, No. 7 (November 2011)
Code
PRM17
Topic
Methodological & Statistical Research
Topic Subcategory
Modeling and simulation
Disease
Multiple Diseases