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.
Carter, Grace M., Joseph P. Newhouse, and Daniel A. Relles, How Much Change in the Case Mix Index Is DRG Creep? Santa Monica, CA: RAND Corporation, 1990. https://www.rand.org/pubs/reports/R3826.html. Also available in print form.
Carter, Grace M., Joseph P. Newhouse, and Daniel A. Relles, How Much Change in the Case Mix Index Is DRG Creep? RAND Corporation, R-3826-HCFA, 1990. As of February 15, 2024: https://www.rand.org/pubs/reports/R3826.html