Weighting case mix groups: the fatal flaw in resource intensity weights.

Resource Intensity Weights (RIWs) for Case Mix Groups (CMGs) are calculated using American Diagnosis Related Group (DRG) weights and Canadian average-length-of-stay data. However, this calculation does not actually "Canadianize" DRG weights; it only serves to randomize them. This article demonstrates the lack of the all-important relationship between RIWs and CMG costs by using simplified graphical examples. Notwithstanding the deficiencies of RIWs, the concept of weighted CMGs is fundamentally sound. Accordingly, until MIS-level reporting is widely implemented and a sufficiently large and reliable domestic database has been accumulated, it may not be entirely inappropriate for Canadian health care institutions to use unadulterated American DRGs for case mix analysis and fiscal planning.