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.