Linking existing instruments to develop a continuum of care measure: accuracy comparison using function-related group classification

Purposes: To compare measurement accuracy of test forms with varied number of items (13, 8, and 4 items) generated from the self-care physical function item bank composed of Functional Independence Measure (FIM™) and the Minimum Data Set (MDS). Methods: Retrospective data analysis of 2499 Veterans who completed both FIM and MDS within 6 days. We compared measurement accuracy between the converted FIM (FIMc) motor score generated from the MDS and the original FIM (FIMa) motor score (13 items) at: (a) individual-level using point differences, and (b) group-level using function-related group (FRG). Results: The differences of mean FIMa and FIMc scores were between 0.05 and 1.07 points for all test forms. Over 81% of FIMc from MDS_13 were within 15 points of the FIMa. 81–90% of FRGs generated by the FIM short forms was identical to those generated by the FIMa for stroke, lower limb amputation, knee and hip replacement; and 59.9–90.5% by all MDS test forms. All MDS test forms had above 74% agreement with same or adjacent FMGs (ICC 0.65-0.91). Conclusions: The accuracy is dependent on the comparison level (i.e., individual or group), length of the test and which FRG is used. Our results partially support using existing instruments—without decreasing the number of the items—to generate a continuum of care measurement.