Mapping functions in health-related quality of life: mapping from the Achilles Tendon Rupture Score to the EQ-5D

PURPOSE: Health state utility values are derived from preference-based measurements and are useful in calculating quality-adjusted life years (QALYs), which is a metric commonly used in cost-effectiveness studies. The purpose of this study was to convert the Achilles Tendon Rupture Score (ATRS) to the preference-based European Quality of Life-5 Dimension Questionnaire (EQ-5D) by estimating the relationship between the two scores using mapping. METHODS: Data were collected from a randomised controlled trial, where 100 patients were treated either surgically or non-surgically for Achilles tendon rupture. Forty-three and forty-four patients in surgical group and non-surgical group completed the ATRS and the EQ-5D alongside each other during follow-up at three time points. Different models of the relationship between the ATRS and the EQ-5D were developed and analysed based on direct mapping and cross-validation. The model with the lowest mean absolute error was observed as the one with the best fit. RESULTS: Among the competing models, mapping based on using a combination of the ATRS items four, five, and six associated with limitation due to pain, during activities of daily living and when walking on uneven ground, produced the best predictor of the EQ-5D score. CONCLUSIONS: The present study provides a mapping algorithm to enable the derivation of utility values directly from the ATRS. This approach makes it feasible for researchers, as well as medical practitioners, to obtain preference-based values in clinical studies or settings where only the ATRS is being administered. The algorithm allows for the calculation of QALYs for use in cost-effectiveness analyses, making it valuable in the study of acute Achilles tendon ruptures. LEVEL OF EVIDENCE: II.