Scoring of health state utility instruments for better comparability

Background: Health state utility (HSU) instruments differ in descriptive system, domains considered, scoring methods, analysis of ordinal data without checking limitations and assumptions of such analysis. A high score indicates higher favorable health state for SF 36, HUI 3, SF 6D, AQoL (response scores)unlike scales like EU-5D-5L, 15 D. Objectives: To provide method for converting item-response scores to continuous, monotonic, normally distributed scores in 1 to 100, avoiding limitations of existing HSU scales with different number of items and different number of levels. Materials and Method: The methodological paper involves no data from patients. Here, health state of an item score is transformed to equidistant-scores by weighted sum where weights are based on frequency of responses to each level of an item. Weights are different for different levels of different items. Standardize Y-scores to Z-scores and convert Z-scores to proposed scores (  in the range 1 to 100. Scale scores as sum of  follows normal distribution. Results: P-scores facilitate inferences like estimation and testing of statistical hypothesis on equality of population parameters either for longitudinal or snap-shot data, assessment of progress/deterioration by a patient or a group of patients. Equivalent score combinations (  to integrate two HSUs were found. Conclusions: The proposed method avoids differences due to descriptive systems, scale effects, utility algorithms, etc. and contributes to improve scoring of HSU instruments avoiding limitations of ordinal scores and facilitating analysis under parametric set up for meaningful comparisons.