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

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.

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.

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.

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.

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.