Reliability and usability of a weighted version of the Functional Comorbidity Index

Purpose: To investigate the reliability of a weighted version of the Functional Comorbidity Index (w-FCI) compared with that of the original Functional Comorbidity Index (FCI) and to test its usability.

Patients and methods: Sixteen physicians collected data from 102 residents who lived in 16 different nursing homes in the Netherlands. A multicenter, prospective observational study was carried out in combination with a qualitative part using the three-step test interview, in which participants completed the w-FCI while thinking aloud and being observed, and were then interviewed afterward. To analyze inter-rater reliability, a subset of 41 residents participated. The qualitative part of the study was completed by eleven elderly care physicians and one advanced nurse practitioner.

Measurements: The w-FCI was composed of the original FCI supplemented with a severity rating per comorbidity, ranging from 0 (disease absent) to 3 (severe impact on daily function). The w-FCI was filled out at baseline by 16 physicians and again 2 months later to establish intra-rater reliability (intraclass correlations; ICCs). For inter-rater reliability, four pairs of raters completed the w-FCI independently from each other.

Results: The ICCs were 0.90 (FCI) and 0.94 (w-FCI) for intra-rater reliability, and 0.61 (FCI) and 0.55 (w-FCI) for inter-rater reliability. Regarding usability of the w-FCI, five meaningful themes emerged from the qualitative data: 1) sources of information; 2) deciding on the presence or absence of disease; 3) severity of comorbidities; 4) usefulness; and 5) content.

Conclusion: The intra-rater reliability of the FCI and the w-FCI was excellent, whereas the inter-rater reliability was moderate for both indices. Based on the present results, a modified w-FCI is proposed that is acceptable and feasible for use in older patients and requires further investigation to study its (predictive) validity.