The Case Mix Groups+ (CMG+) methodology is designed to aggregate acute care inpatients with similar clinical and resource-utilization characteristics. The CMG+ methodology was introduced in 2007 and was designed to take advantage of the increased clinical specificity of ICD-10-CA and CCI.  This methodology, developed using multiple years of acute care inpatient activity and cost records, introduces and enhances several grouping factors to improve the ability to clinically group inpatients and to define length of stay and resource use indicators.

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ICD-10-CA diagnosis codes are used to broadly categorize patients into major clinical categories (MCC). These broad categories are based generally on the most responsible diagnosis code (MRDx). This diagnosis is the one determined to have been responsible for the greatest portion of the patient’s length of stay. The MCC is divided into two partitions: intervention and diagnosis. If a case is assigned to the diagnosis partition of an MCC, a list of diagnosis codes is used to assign the CMG cell. If a case is assigned to the intervention partition of an MCC, a hierarchical list of intervention codes is used to assign the CMG cell.

The CMG+ methodology further refines CMG with components known as factors to reflect additional conditions that influence a patient’s overall medical condition and resource consumption. These factors applied across most CMG include:

  • Age Group
  • Comorbidity Level
  • Flagged Interventions
  • Intervention Events
  • Out-of-Hospital Intervention

Together, these factors are applied to the acute care inpatient cases to improve estimates of resource indicators (RIW and ELOS).


The CMG+ methodology will allow hospitals to predict length of stay and resource use more accurately for:

  • Planning and evaluating programs
  • Analyzing physician impact
  • Translating case mix data into estimated costs
  • Monitoring clinical practice and resource use
  • Developing benchmarks


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