Comparing the Functional Independence Measure and the interRAI/MDS for use in the functional assessment of older adults
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Background: The rehabilitation of older persons is often complicated by increased frailty and medical complexity – these in turn present challenges for the development of health information systems. Objective investigation and comparison of the effectiveness of geriatric rehabilitation services requires information systems that are comprehensive, reliable, valid, and sensitive to clinically relevant changes in older persons. The Functional Independence Measure is widely used in rehabilitation settings – in Canada this is used as the central component of the National Rehabilitation Reporting System of the Canadian Institute of Health Information. An alternative system has been developed by the interRAI consortium. We conducted a literature review to compare the development and measurement properties of these two systems and performed a direct empirical comparison of the operating characteristics and validity of the FIM motor and the ADL items on the PAC in a sample of older adults receiving rehabilitation. Methods: For the first objective english language literature published between 1983 (initial development of the FIM) and 2008 was searched using Medline and CINAHL databases, and the reference lists of retrieved articles. Additionally, attention was paid to the ability of the two systems to address issues particularly relevant to older rehabilitation clients, such as medical complexity, comorbidity, and responsiveness to small but clinically meaningful improvements. For the second objective we used Rasch analysis and responsiveness statistics to investigate and compare the instruments dimensionality, item difficulty, item fit, differential item function, number of response options and ability to detect clinically relevant change. Results: The majority of FIM articles studied inpatient rehabilitation settings; while the majority of interRAI/MDS articles focused on nursing home settings. There is evidence supporting the reliability of both instruments. There were few articles that investigated the construct validity of the interRAI/MDS. The analysis showed that the FIM may be slightly more responsive than the PAC, especially in the MSK patients. However, both scales had similar limitations with regards the large ceiling effect and many unnecessary response options. Conclusions: Additional psychometric research is needed on both the FIM and MDS, especially with regard to their use in different settings and ability to discriminate between subjects with functional higher ability.