Weighted index explained more variance in physical function than an additively scored functional comorbidity scale.

Objective: 1) examine association between the Functional Comorbidity Index (FCI) and discharge functional status (FS); 2) examine impact of FCI on FS when added to comprehensive models; and 3) compare additive FCI with weighted FCI and list of condition variables (list).

Study Design And Setting: Patients were drawn from Focus On Therapeutic Outcomes, Inc. (FOTO) database (1/1/06-12/31/07). FS collected using computer adaptive tests. Linear regression examined association between FCI and FS. Three methods of including functional comorbidities (FC) were compared.

Results: Relationship between FCI and FS varied by group (range, 0.02-0.9). Models with weighted index or list had similar R². Weighted FCI or list increased R² of crude models by <0.01 for cervical, shoulder, and lumbar; by 0.01 for wrist/hand, knee, and foot/ankle; by 0.02 for hip; by 0.03 for elbow; and by 0.08 for neurological. Addition of FCI to comprehensive models added <0.01 to R² (all groups). Weighted FCI increased R² by <0.01 for cervical, lumbar, and shoulder; by 0.01 for wrist/hand, hip, knee, and foot/ankle; by 0.02 for elbow; and by 0.04 for neurological; whereas list increased R² by <0.01 for cervical, shoulder, and lumbar; by 0.01 for knee and foot/ankle; by 0.02 for elbow, wrist/hand, and hip; and by 0.05 for neurological.

Conclusion: List of comorbidities or weighted FCI is preferable to using additive FCI.