The authors reabstracted a nationally representative sample of 7,887 Medicare charts to determine how much of the change in Medicare's Case Mix Index between 1986 and 1987 was due to upcoding or DRG (diagnosis-related group) creep. About two-thirds of the actual change is true. Most of the remaining third is attributable to a general change in the completeness of coding; some is attributable to changes in the Grouper program that assigns DRGs to cases using diagnostic and procedural information. Thus, most of the additional $1 billion that Medicare paid to hospitals because of the change in the Case Mix Index appears justified by the additional complexity of the cases of the patients being hospitalized.
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