Providing an extended use of an otological-specific outcome instrument to derive cost-effectiveness estimates of treatment

Objectives: Although Quality-Adjusted Life Years (QALYs) are increasingly being used by decision makers to make comparisons of cost-effectiveness, there are no otological-specific outcome measures that fit within this QALY framework. This study had two main objectives. The first was to provide a means to derive QALYs from a condition-specific otological instrument (COQOL) and the second, was to assess the convergent validity, or degree of correlation, between the COQOL and SF-6D, an established QALY instrument. Design: Longitudinal cohort study designed to assess the convergent validity between SF-6D and COQOL, and to generate a mapping function to enable SF-6D values to be predicted from the COQOL responses. Setting: Cambridge University Hospital, UK Participants: 207 patients attending a routine outpatient general otology clinic. Main outcome measures: SF-6D and the COQOL instrument completed at baseline, and again 3 months later. Results: Convergent validity was demonstrated with mean SF-6D values decreasing linearly with increasing severity on the COQOL instrument. Overall, the correlation between the COQOL scores and the SF-6D values was moderate and statistically significant (r=.490, p=<0.001). A simple mapping model based on an Ordinary Least Squares regression function predicted SF-6D values from the COQOL data with a reasonable degree of accuracy. Further validation using the follow up 3-month data confirmed the prediction power of this mapping model. Conclusions: This study provides a method for estimating QALYs from condition-specific COQOL data and provides the opportunity for the cost-effectiveness of otological treatment to be measured and placed within the national QALY framework.