Mapping the Functional Independence Measure to a multi-attribute utility instrument for economic evaluations in rehabilitation: a secondary analysis of randomized controlled trial data
Purpose: To test whether the Functional Independence Measure (FIM) could be mapped to the EQ-5D-3L to give researchers a viable but "second-best" option for calculating quality-adjusted life-years (QALYs) and conducting a cost-utility analysis when only clinical outcomes have been collected.Materials and methods: Secondary analysis of repeated measures data collected during a randomized controlled trial (n = 3506 observations) at two inpatient rehabilitation centres. Participants had a mean age of 74 (SD 13) years, 63% were women and 58% were admitted with an orthopaedic diagnosis. Ordinary least-squares regression and adjusted limited dependent variable mixture models were used to estimate regression-based mappings. Performance was evaluated based on mean absolute error and the proportion of errors in excess of the minimally important difference.Results: In orthopaedic and neurological patients, high mean absolute errors (0.2 on the quality-adjusted life years scale) and a high proportion of errors (60%) in excess of the minimally important difference suggest that predicted EQ-5D-3L values provided a poor substitute for observed EQ-5D-3L values.Conclusions: Regression-based mappings from the FIM to the EQ-5D-3L are error-prone and unsuitable for calculating QALYs in rehabilitation patients. Researchers and rehabilitation professionals should therefore include a multi-attribute utility instrument such as the EQ-5D as well as the FIM to evaluate the effect of rehabilitation interventions and in rehabilitation registries. This will provide additional information on health-related quality of life and support cost-utility analyses.Implications for rehabilitationThe Functional Independence Measure (FIM) cannot be used to calculate quality-adjusted life-years (QALYs) for cost-utility analyses.Predicting QALYs from FIM data is a poor substitute for direct measurement of QALYs in orthopaedic or neurological rehabilitation populations.Multi-attribute utility instruments (MAUIs) allow direct measurement of QALYs, as well as providing a patient-reported measure of clinical quality and outcomes in rehabilitation.A MAUI should be included routinely in clinical practice by rehabilitation professionals as well as in rehabilitation trials and registries to track patient outcomes and improve clinical practice.