Multimorbidity Indices in Adults: A Systematic Review of Data Frameworks, Weighting Methods, and Applications

To understand the burden of multimorbidity is a key concern in both clinical care and policy decision-making. However, the rapid growth of multimorbidity indices has led to wide variations in their purpose, design, scope and applicability across settings. This systematic review synthesizes current evidence on the development and use of multimorbidity indices, with a focus on their predictive performance for clinical outcomes and health service use.

A systematic search was conducted in PubMed, Web of Science, and Scopus for studies published between 2000 and 2025 (CRD 420250653881). Eligible studies examined adults with at least two chronic conditions using index-based approaches to predict clinical and health service use outcomes. Data were extracted on study design, population characteristics, index variables, statistical methods, and validation metrics.

A total of 63 pivotal studies were identified, mainly from the US (37%), the UK (11%), and Canada (8%). Most aimed to predict overall health or functional status (75%), mortality (60%), and healthcare use (60%). Common indices included the Charlson Comorbidity Index (CCI, n = 17), Multimorbidity-Weighted Index (MWI, n = 12), and Cumulative Illness Rating Scale (CIRS, n = 10). Frequently used typologies included Disease-Specific Weighting, Simple Disease Count, and Severity-Based Weighting. While nearly all indices covered physical chronic conditions, fewer than 20% considered mental health disorders. Validation often relied on C-statistics, ranging from 0.66 to 0.931, and 43% of studies focused on validating existing indices. Several indices are now referenced in clinical guidelines and policy frameworks, demonstrating their value in system planning and patient risk stratification.

Current multimorbidity indices reveal gaps in scope and methodological consistency. Their limited attention to mental health underscores a narrow framing of disease burden. Though widely applied in clinical and policy contexts, the lack of standardized reporting hinders broader adoption and integration.