Concept: Case Mix Groups (CMGs™) versus Diagnosis Related Groups (DRGs™)

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Concept Description

Last Updated: 2001-03-22


    1. Case Mix:

      Both are patient classification systems that provide ways of describing the types of patients a hospital treats (its case mix).
      • group cases into manageable number of meaningful patient categories
      • patients within each category are similar clinically and in terms of resource use
      • use administrative data to group cases
      • algorithm of DRG™/CMG™ assignments is identical except that CMGs™ were designed to be grouped according to the most responsible diagnosis

      Diagnoses 01 to 25: mutually exclusive categories based on body systems.
      • within each category cases separated into medical and surgical.
      • then CMG™/DRG™ assigned.

    2. Weights:

      Both CMGs™ and DRGs™ have weights associated with them that are supposed to reflect the relative costs for each group.
      • RIWs™: Resource Intensity Weights are the weights associated with CMGs™. They are based on charge data from Maryland and Canadian LOS
      • Available from CIHI with CMG™ grouper
      • DRG™ weights: weights associated with DRGs™ based on Medicare patients only; available from the USA

    3. Complexity / Intensity of Refinement:

    • RDRGs® - for DRGs™
    • Complexity overlay - for CMGs™

      These two refinements are very similar - CMGs™ also have age adjustment factor.

      Weights available for complexity/intensity refinement:
      • RDRG® weights developed at MCHP for RDRGs®.
      • RIWs™ for complexity overlay.
    1. Cautions:

    • Unlike DRGs™, CMGs™ may change number from one year to the next. This can create problems for longitudinal studies.

    2. Complications and Comorbidities:

    • With CMG™ - they use diagnosis typing - can distinguish between a comorbidity (pre-existing additional diagnosis) and a complication (diagnosis that arose after admission). (DRG™ - comorbidities and complications are grouped together).

    3. Out-patients:

Related concepts 

Related terms 


  • classification
  • complications
  • Health Measures

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