Mapping the Shah-modified Barthel Index to the Health Utility Index Mark III by the Mean Rank Method

To map the Shah-modified Barthel Index (SBI) to the Health Utility Index Mark III (HUI-3) in stroke patients, and to compare the performance of a recently developed method called the Mean Rank Method (MRM) against a popular method, the Ordinary Least Squares (OLS) method.

A cohort of 473 patients who had their first clinical stroke diagnosis and hospital admission and were assessed using the SBI and HUI-3 at 3 months and/or 12 months post-admission. Observations were split to form a training dataset (N = 473) and a validation dataset (N = 245).

In the training dataset, the MRM using SBI total score as the predictor produced a mapped utility distribution that closely resembled the observed utility distribution. It had almost no shrinkage of the standard deviation (P = 0.542), whereas the OLS using SBI total score and SBI item scores under-estimated the standard deviation by 28% and 26%, respectively (each P < 0.001). The MRM mapping gave better fit in terms of smaller mean absolute error and larger intra-class correlation than the two versions of OLS mapping, whereas the OLS gave smaller mean-squared errors than the MRM. Multivariate regression analysis showed that the use of OLS-mapped utilities tended to under-estimate both the mean utility of people who had no comorbidity and the utility-comorbidity association as compared to the observed utility-comorbidity pattern although the differences did not reach statistical significance (each P > 0.05). The MRM-mapped utility showed utility-comorbidity pattern more similar to the observed. Similar findings were obtained from the validation dataset.

The MRM performed well. Mapping functions are available to map the SBI to the HUI-3 Utility Index.