Skip to Sub-navigation

Case-mix grouping methodologies help health care facilities plan and manage their services

CIHI has taken a lead role in developing and implementing case-mix methodologies to categorize patients into statistically and clinically homogeneous groups based on the collection of clinical and administrative data. CIHI’s case-mix methodologies are used by hospitals, health regions and ministries of health to help monitor and improve the care and services provided. Understanding the different care requirements of patients forms the basis for comparing health care organizations and case mix–adjusted resource use.

Canadian health care managers, clinicians and other health professionals face the increasingly difficult challenge of reducing costs while maintaining or improving quality of care and access. By sorting information about each patient into similar categories, case-mix groupings help health care facilities better understand the populations being cared for in order to meet their individual needs. 

Sorting Out Case Mix External link, opens in new window
This video explains how sorting information about each person into similar categories - or case mix groupings - can help us better understand the populations we're caring for and meet their individual needs.

Case Mix in Action External link, opens in new window
This video explains how CIHI’s case-mix methodologies are used by hospitals, health regions and ministries of health to help monitor and improve the care and services provided.

Grouping methodologies

Case mix supports a number of different grouping methodologies for populations, areas of care and assessment data.

Population grouping methodology

  • The population grouping methodology (PDF) assigns clinical profiles and resource utilization indicators to all persons in the population. The methodology uses inpatient, day surgery, physician billing and long-term care data.
  • As described in the population grouping methodology video External link, opens in new window, clinical and demographic profiles for each person in a population are created, including profiles for health system non-users. This information is then used to predict health care utilization patterns, explain variations in health care resource use and provide a foundation for funding models.

  • For more information, including how to access the population grouping methodology, please write to

Acute inpatient grouping methodology

  • CMG+
    A refinement of the Case Mix Groups methodology. It aggregates acute care inpatients with similar clinical and resource utilization characteristics.
  • Resource Intensity Weights (RIWs) and Expected Length of Stay (ELOS)
    ELOS is the average acute length of stay in hospital for patients with the same Case Mix Group (CMG), age category, comorbidity level and intervention factors. RIW is a relative value measuring total patient resource use compared with average typical acute inpatients.
  • Case Mix Decision-Support Guide: CMG+
    A summary of the CMG+ grouping and indicator methodology. It also includes guidelines for using case-mix information for decision support as well as analytical techniques for using case-mix data.
  • Assigning HIG Weights and ELOS Values to Ontario Inpatient DAD Cases
    Provides an explanation of the ELOS calculation and the Health Based Allocation Model (HBAM) Inpatient Group (HIG) Weight calculation for typical and atypical acute care inpatient cases.

Acute ambulatory care grouping methodology

Continuing and specialized care grouping methodologies

Case mix also supports grouping methodologies for continuing and specialized care.

Continuing Care Reporting System (CCRS)

Resource Utilization Groups version III Plus

The RUG-III Plus case-mix system is applicable to both the Continuing Care Reporting System (CCRS) and the Integrated interRAI Reporting System (IRRS).

Resource Utilization Group, version III (RUG-III)

This grouping methodology is applied to RAI-MDS 2.0 Canadian version assessment data submitted to CCRS. Effective 2011, the CCRS RUG-III (44-group) Case Mix Index (CMI) values will no longer be a separate product; they are available only with the complete CCRS RUG-III grouper product.

Resource Utilization Group Weighted Patient Day (RWPD) reports

Resource summary reports produced for complex continuing care and long-term care at the resident level.

Resource Utilization Group version III, Home Care (RUG-III-HC)
This grouping methodology is applied to Resident Assessment Instrument–Home Care (RAI-HC) Canadian version assessment data submitted to the Home Care Reporting System.

Rehabilitation Patient Groups (RPGs)

A grouping methodology applied to episodes based on the FIM® instrument data submitted to the National Rehabilitation Reporting System (NRS)

System for Classification of In-Patient Psychiatry (SCIPP)

A grouping methodology applied to Minimum Data Set–Mental Health (MDS-MH) assessment

Databases related to case mix

Canadian MIS Database 
The Canadian MIS Database  (CMDB) is the national data source for financial and statistical information about hospitals and health regions. The day-to-day health service operations data is collected according to a standardized framework known as the Standards for Management Information Systems in Canadian Health Service Organizations (MIS Standards).

Continuing Care Reporting System 
The Continuing Care Reporting System (CCRS) contains demographic, clinical, functional and resource utilization information on individuals receiving continuing care services in hospitals or long-term care homes in Canada. Participating organizations also provide information on facility characteristics to support comparative reporting and benchmarking.

Discharge Abstract Database 
The Discharge Abstract Database (DAD) contains demographic, administrative and clinical data on inpatient hospital discharges. Facilities in all provinces and territories except Quebec are required to report to the DAD. Quebec acute inpatient records are submitted to CIHI through a different process and are included in the Hospital Morbidity Database.

Home Care Reporting System 
The Home Care Reporting System (HCRS) contains demographic, clinical, functional and resource utilization information on clients served by publicly funded home care programs in Canada.

National Ambulatory Care Reporting System 
The National Ambulatory Care Reporting System (NACRS) contains data for all hospital-based and community-based ambulatory care: day surgery, outpatient clinics and emergency departments. Client visit data is collected at the time of service in participating facilities.

National Rehabilitation Reporting System 
The National Rehabilitation Reporting System (NRS) contains client data collected from participating adult inpatient rehabilitation facilities and programs across Canada, including specialized facilities and hospital rehabilitation units, programs and designated rehabilitation beds.

Ontario Mental Health Reporting System 
The Ontario Mental Health Reporting System (OMHRS) contains data about individuals admitted to adult mental health beds in the province of Ontario. It includes information about their mental and physical health, as well as which social supports and services they use. The data is collected at admission, discharge and every three months for patients with extended stays.

Related resources on case mix

Listed below you’ll find a sample of CIHI’s education courses on case mix. Check out the job aid (PDF) on how to access these courses. You can register for any of these, or learn more about CIHI’s other courses, by visiting our Learning Centre.


Continuing and specialized care

  • CCRS Case Mix Fundamentals of RUG-III and RWPD
  • Calculating RUG-III (44-Group)
  • Introduction to the Rehabilitation Patient Group (RPG) Methodology for NRS
  • Introduction to RUG Weighted Patient Days for Ontario CCRS
  • OMHRS SCIPP Methodology and SCIPP Weighted Patient Day (SWPD) Report Interpretation

Regrouping historical data

Regrouping historical data is the process of assigning the most recent grouping methodology and resource indicators to historical data. The Regrouped Historical Data—CIHI Reference Document provides information about this regrouped historical data process.

Information sheet