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Reliability of a comorbidity measure: the Index of Co-Existent Disease (ICED)
K Imamura1, M McKinnon, R Middleton
1Dept. of Public Health and Policy, London School of Hygiene & Tropical Medicine, UK.
Insights
The Index of Co-Existent Disease (ICED) shows moderate reliability for assessing comorbidities in elderly hip replacement patients. Improving ICED instructions is crucial for consistent application in retrospective data analysis.
Area of Science:
- Geriatric Medicine
- Health Services Research
- Medical Informatics
Background:
- Comorbidity indices are vital for predicting patient outcomes and guiding clinical decisions.
- The Index of Co-Existent Disease (ICED) is an established tool for quantifying patient comorbidities.
- Accurate comorbidity assessment is essential, particularly in elderly populations undergoing major surgery.
Purpose of the Study:
- To evaluate the inter-rater and intra-rater reliability of the Index of Co-Existent Disease (ICED).
- To assess the reliability of the ICED using retrospective data from elderly patients undergoing total hip replacement.
- To identify factors contributing to the reliability of the ICED in clinical practice.
Main Methods:
- Retrospective analysis of case notes from elderly patients who underwent total hip replacement.
- Two inter-rater reliability assessments with two and three raters, respectively.
- One intra-rater reliability assessment using a single rater.
Main Results:
- Moderate inter-rater reliability for the overall ICED (kappa 0.5-0.6).
- Excellent intra-rater reliability (kappa 0.9).
- The Functional Severity subindex showed good reliability (kappa 0.6-1.0), while the Index of Disease Severity subindex had lower reliability (kappa 0.4-0.5).
- Rater discrepancies influenced the association between comorbidity and post-operative complications.
Conclusions:
- The ICED demonstrates moderate reliability in assessing comorbidities, with significant variations in inter-rater consistency.
- Intra-rater reliability is high, suggesting individual raters can apply the index consistently.
- Enhancements to ICED instructions are necessary to improve inter-rater reliability for retrospective data analysis.
Abstract:
The reliability of an established comorbidity index (the Index of Co-Existent Disease) was tested using retrospective data from the case notes of elderly patients who had undergone total hip replacement. Inter-rater reliability was examined twice, first with two raters (n = 39) and then with three (n = 49). Intra-rater reliability was assessed using one rater (n = 45). Reasons for any lack of reliability were explored. The inter-rater reliability of the ICED was moderate (kappa 0.5-0.6). While the Functional Severity index performed well (kappa 0.6-1.0), the Index of Disease Severity subindex was less reliable (kappa 0.4-0.5). Differences between raters had an impact on the observed association between comorbidity and serious post-operative complications. Intra-rater reliability was excellent (kappa 0.9). Several reasons why inter-rater reliability was only moderate were identified, mostly related to uncertainties in applying the ICED. The reliability of the ICED needs to be improved before it is used more widely with retrospective data. This might be achieved by further clarification of the instructions for its use.