The structure of the Early Rehabilitation Barthel Index (ERBI) should be modified: evidence from a Rasch analysis study

BACKGROUND: The Early Rehabilitation Barthel Index (ERBI) comprises seven items of the Early Rehabilitation Index and ten items of the Barthel Index. The ERBI is usually used to measure functional changes in patients with severe acquired brain injury (sABI), but its measurement properties have yet to be extensively assessed.AIM: To study the unidimensionality and internal construct validity (ICV) of the ERBI through Confirmatory Factor Analysis (CFA), Mokken Analysis (MA), and Rasch Analysis (RA).DESIGN: Multicenter prospective study.SETTING: Inpatients from five intensive rehabilitation centers.POPULATION: Two hundred and forty-seven subjects with sABI.METHODS: ERBI was administered on admission and discharge to study its unidimensionality through CFA and MA and its ICV, reliability, and targeting through RA.RESULTS: The preliminary analyses showed a lack of unidimensionality (RMSEA=0.460 >0.06; SRMR=0.176 >0.06; CFI=1.000 >0.950; TLI=1.000 >0.950). According to CFA, "Confusional state" and "Behavioral disturbance" items showed low factor loadings (<0.40), whereas these two items composed a separate scale within the MA. Furthermore, the baseline RA showed that three items misfitted ("Mechanical ventilation," "Confusional state," "Behavioral disturbances") and a lack of conformity of several ICV requirements. After deletion of three misfitting items and further non-structural modifications (i.e., testlets creation to absorb local dependence between items and item misfit), the solution obtained showed adequate ICV, adequate reliability for measurements at the individual level (PSI>0.85), although with a frank floor effect. This final solution was successfully replicated in a total sample of the subjects. After post-hoc modifications of the score structure of two out of three misfitting items, the subsequent CFA (RMSEA=0.044 <0.06; SRMR=0.056 <0.06; CFI=1.000 >0.950 TLI=1.000 >0.950) and MA showed the resolution of the unidimensional issues.CONCLUSIONS: Although the ERBI is a potentially valuable tool for measuring functioning in the coma-to-community continuum, our analyses suggested its lack of ICV, partly due to an incorrect scoring design of some items. A new perspective multicenter study is proposed to validate a modified version of the ERBI that overcomes the problems highlighted in this analysis.