Four methods for characterizing disability in the formation of function related groups

The Functional Independence Measure-Function Related Groups (FIM-FRGs) were developed to classify medical rehabilitation inpatients into homogeneous groups based on length of stay (LOS). Patients are first grouped into clinically relevant rehabilitation impairment categories, then by functional status, as expressed by the FIM, and in certain cases by patient age. The statistical approach used to form the final groupings was a recursive partitioning algorithm applied to the FIM scores and patient age within impairment category. This analysis compares four FIM-FRG classification schemes developed from four scale sets that combine FIM items differently: (1) use of the 18 FIM items as separate variables, (2) the combination of FIM items into six clinical subscales, (3) the combination of the six clinical subscales into motor and cognitive subscales, and (4) the combination of all FIM items into a single scale. The FIM-FRG schemes explain similar amounts of variance in the logarithm of LOS and contain approximately equal numbers of FRGs. The motor and cognitive subscale scheme is recommended for use in payment, however, this scheme and the other schemes have additional uses. Each FRG scheme provides different insight into the clinical relationship between disability and LOS.