This is Bob. Bob is newly admitted to the hospital with pneumonia. Pneumonia will map to an ICD code which in turn will map to a diagnostic related group, or DRG. Each DRG is assigned a relative weight which allows for a grading, or ranking, of condition based on the severity of the condition. Secondary diagnoses can contribute to the overall weight of the DRG when categorized as a CC(comorbidity or complication) or an MCC(major...). Bob has some complicating risk factors...smoking, drinking, poor diet, obesity... which in turn can complicate his stay as COPD, cirrhosis, hyperlipidemia, CAD. This increased complexity should also be reflected in the "weight" of his DRG; Sepsis, an MCC, even more so.
Weight can also be aggregated to reflect the complexity of our patient population. This is called case mix index, or CMI. CMI can be calculated for the entire hospital, a specific hospital service , or even a specific provider.
SFGH uses a data clearinghouse to manage our JC and CMS reporting. UHC also allows us to compare ourselves to other academic medical centers... and when we compare our CMI we find our selves in the lower quartile.