Interhospital Differences in the Severity of Illness

To the Editor: Horn et al. (July 4 issue)¹ address a timely and important issue by asking whether Medicare's case-mix index, based on DRGs (diagnosis-related groups), fairly reflects the treatment needs of Medicare beneficiaries. The authors argue that because a case-mix index adjusted by the severity-of-illness index does not correlate perfectly with Medicare's case-mix index, Medicare's index does not take adequate account of severity of illness. They are to be commended for going directly to medical records for their data. However, we should be quite cautious in drawing conclusions from their data and even more cautious in concluding that the.