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	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

To The Editor.—Dr Howard and colleagues¹ correctly emphasize that studies comparing surgical vs nonsurgical therapy pose distinctive statistical challenges because the complications of surgery usually occur early, whereas the complications of nonsurgical therapy generally occur at a constant rate over time. However, other inherent differences between surgical and nonsurgical therapies can invalidate comparisons between them despite the most careful statistical adjustments.²

Drug therapy is constant throughout the duration of a study since the chemical compound does not change, whereas surgical technique evolves continuously. The operation being used by the end of a study can differ markedly from the one with which the study began. Thus, increased experience with surgery improves results and decreases complication rates, whereas increased use of drugs usually unveils more complications. In one study, the mortality of coronary bypass surgery decreased from 3 (12%) of 25 patients in 1968 to 2 (1.5%) of 134 patients in . . . [Full Text of this Article]

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RELATED ARTICLE

Assessing Differences in Clinical Trials Comparing Surgical vs Nonsurgical Therapy: Using Common (Statistical) Sense
George Howard, Lloyd E. Chambless, and Richard A. Kronmal
JAMA. 1997;278(17):1432-1436.
ABSTRACT