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

SIMILARITIES

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.

DIFFERENCES

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:


• DPGs - (Day Procedure Groups) outpatient grouper and weights are available from CIHI. For more information, please see the CIHI Web Site at: https://www.cihi.ca/en/data-and-standards/standards/case-mix/day-procedure-groups-dpg .