Case Mix Group+ (CMG+) is an inpatient grouping methodology based on ICD-10-CA and CCI codes and selected data elements from the Discharge Abstract Database (DAD). It categorizes patients into statistically and clinically homogeneous groups.
Overview of the methodology
CMG+ categorizes patients into statistically and clinically homogeneous groups. It also assigns 2 indicators: Expected Length of Stay (ELOS) and Resource Intensity Weight (RIW). An overview of the process for calculating the indicators, along with examples, is provided in the DAD RIW and ELOS manual.
The Health Based Allocation Model (HBAM) Inpatient Group (HIG) is an Ontario-specific inpatient grouping methodology based on CMG+. This methodology groups Ontario inpatient data originating from the DAD and assigns HIGs that are specific to the Ontario Ministry of Health.
Accessing the methodology
The CMG+ Directory is a reference guide to the grouping methodology that includes detailed information on CMGs and the associated factor methodology assigned to inpatients. The CMG+ directories for the last 4 fiscal years are available in CIHI’s eStore. The next release of the CMG+ Directory is expected to be in 2027.
- CMG+ Directory (download)
- Requirement for Downloading Case Mix Files
- Case Mix Group+ for typical patients (job aid)
CMG client tables provide common case-mix information in tab-delimited ASCII format that can be used for analysis. CMG client tables include the following:
- Descriptions of major clinical categories (MCCs), CMGs, Flagged Intervention (FI) groups and statuses, and RIW atypical categories, which can be linked to data grouped with the associated CMG methodology year
- CCI intervention partition list of all interventions considered for assignment to the intervention partition
- Comorbidity and FI code finders, and comorbidity count and comorbidity interaction factor tables, which can be used to better understand how Comorbidity Level and FI categories are derived
- CMG ELOS and RIW factor tables, which allow for a better understanding of how these variables are calculated
- Descriptions of values and aggregate CMG variable assignments for the variables High-Level (HL) CMG, CMG Care Level and CMG Provider Service, which can be linked to acute care data in the DAD
- Trending tables at the level of CMG, HL CMG, CMG Care Level and CMG Provider Service with 3 years of DAD volumes by jurisdiction, which can be used for decision support
- Functional Area CMG RIW proportion tables, which can be used in combination with RIWs to estimate resource use per functional area for each CMG
The CMG client tables and the DAD RIW and ELOS document are available for download in CIHI’s eStore:
The HIG client tables and the HIG weights and ELOS documents are available for download in CIHI’s eStore:
Methodology in action
- Decision-Support Guide: CMG+ (download): CMGs and the indicator methodology can be used to analyze utilization and trends, and for decision support. Annually, when a new version of the CMG+ methodology is released, the most recent 5 years of data are regrouped and provided to stakeholders to allow for trending in a common methodology year. The Decision-Support Guide provides a summary of the CMG+ and RIW methodology, guidelines for using case-mix information for decision support and analytical techniques for using case-mix data.
- Introduction to CMG+ Aggregation Variables (PDF): CMG aggregation variables have many uses, including the ability to facilitate analyses when CMG volumes are small. The 530 CMGs have been assigned to 91 higher-level categories. Additionally, CMGs have been aggregated to 3 CMG Care Levels: highly specialized, specialized and general. Finally, CMG Provider Service categorizes CMGs by the provider most responsible for the care of patients in each group, and CMG Provider Service Groups aggregates each service into even broader categories such as family medicine and surgery.
- Patient Cost Estimator (PCE): This interactive tool combines case-mix and hospital financial data to estimate the average typical CMG costs by jurisdiction. The PCE also lets users search with common terms if they aren’t familiar with CMGs.
CIHI also helps with designing and implementing activity-based funding or other evidence-based funding models using CMG+ by producing reports and analyses:
Education materials
- Case Mix Education (job aid) (PDF)
- Education Roadmap (PDF)
- Understanding How CMG+ Works
- Introduction to Resource Indicators (RIW and ELOS) for DAD and NACRS
- Classifications and Grouping Methodologies: v2022 Points of Interest for Reporting and Analysis
- Introduction to HIG Grouping and Weighting Methodology for Ontario
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