Societal Utilities for Cognitive Impairment in Schizophrenia: Developing a Preference-Based Scoring Algorithm Based on the Schizophrenia Cognition Rating Scale.

Abstract

Loss of cognitive function is a common feature in schizophrenia. However, generic measures of health-related quality of life favored by decision-makers, such as the EQ-5D, are not designed to detect changes in cognitive function. We report the valuation of the Schizophrenia Cognition Rating Scale (SCoRS), a schizophrenia-specific measure of cognitive impairment. Expert opinion and psychometric analysis of the SCoRS from clinical trial data was undertaken to select 5 key items from the measure. These items were combined orthogonally to develop health-state vignettes. Vignettes were valued using composite time trade-off (cTTO) in one-on-one video calls. Several econometric models were fitted to the data to estimate disutilities. Performance of EQ-5D- and SCoRS-based utilities were compared in the trial data. The SCoRS items selected for the valuation study represented attention, learning, processing speed, social cognition and memory. Four hundred respondents participated in the valuation study. The best observed health state was valued at 0.855 [standard deviation (SD)=0.179] and the worst at 0.152 (SD=0.575). At the most severe levels, 'social cognition' received the largest disutility followed by 'learning' and 'memory'. The final model to estimate utilities had 15 parameters. SCoRS-based utilities were sensitive to change in cognition, but the EQ-5D was not. It is feasible to value different dimensions of cognition separately using a validated instrument for proxy assessment. The resulting utilities indicate loss of quality of life due to reduced cognitive functioning.