Objective To compare the test-retest reliability and random measurement errors of the Barthel Index (BI) and modified Barthel Index (MBI) in patients with chronic stroke. Method The intraclass correlation coefficient (ICC) and the minimal detectable change (MDC) were applied respectively to examine the test-retest reliability (about 2 weeks apart) and the random measurement errors. The MDC% was used to adjust the cut-off score for determining whether a real change had been achieved, if heteroscedasticity existed. Results A total of 60 patients participated. The BI and MBI both had high ICCs (0.94 and 0.94, respectively) with small MDCs (16.2 and 15.4, respectively) and MDC%s (21.2% and 19.0%, respectively), indicating that both measures have comparable reliability in repeated assessments. However, moderate associations (r= -0.47 for the BI and -0.59 for the MBI) were found between the means of tests and retests and the absolute values of change scores, indicating heteroscedasticity. These findings suggest that a fixed MDC value is not appropriate for determining the real change in both measures because the amount of random measurement error varies with the patients' ADL function. Conclusion The MBI, which showed excellent test-retest reliability and relatively lower random measurement error than the BI, appears to be a better ADL measure. The MDC% adjusted value is recommended to determine whether the change scores are beyond random measurement error.
