HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Gerald S. Weinstein Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Weinstein, G. S. Articles by Levin, B. Search for Related Content PubMed PubMed Citation Articles by Weinstein, G. S. Articles by Levin, B.

Ann Thorac Surg 1989;48:490-495
© 1989 The Society of Thoracic Surgeons

---

Articles

Effect of Crossover on the Statistical Power of Randomized Studies

Division of Cardiothoracic Surgery, Long Island Jewish Medical Center, New Hyde Park, New York
the Division of Biostatistics, Columbia University School of Public Health, New York, New York

Accepted for publication March 31, 1989.

^* Address reprint requests to Dr Weinstein, Division of Cardiothoracic Surgery, Long Island Jewish Medical Center, New Hyde Park, NY 11042

Randomized studies involving long-term follow-up are vulnerable to the effects of unplanned crossover. In surgical studies, such crossover usually occurs when control patients become more symptomatic and undergo operation. In several large studies of coronary bypass grafting, crossover ranged from 25% to 38%. The most common way of dealing with this problem is to apply the "intention-to-treat" principle, which analyzes such crossovers with their originally assigned groups. Besides the logical problem of counting a control patient who actually undergoes operation as "nonsurgical," a more subtle problem arises in terms of statistical power. When statistical power is low, a truly effective treatment may be mistakenly labeled as no better than control, causing a potentially valuable form of therapy to be ignored or discarded. This analysis demonstrates that crossover may have a profound effect on the statistical power of randomized studies and presents a method for predicting the effect of such crossover on statistical power.

This article has been cited by other articles:

				L. W. Sherman and H. Strang Verdicts or Inventions?: Interpreting Results from Randomized Controlled Experiments in Criminology American Behavioral Scientist, January 1, 2004; 47(5): 575 - 607. [Abstract] [PDF]

				G. W. Torrance, M. F. Drummond, and V. Walker Switching Therapy in Health Economics Trials: Confronting the Confusion Med Decis Making, July 1, 2003; 23(4): 335 - 340. [Abstract] [PDF]

				P. R. GARTIN Dealing with Design Failures in Randomized Field Experiments: Analytic Issues Regarding the Evaluation of Treatment Effects Journal of Research in Crime and Delinquency, November 1, 1995; 32(4): 425 - 445. [Abstract] [PDF]

				L. W. SHERMAN Defiance, Deterrence, and Irrelevance: A Theory of the Criminal Sanction Journal of Research in Crime and Delinquency, November 1, 1993; 30(4): 445 - 473. [Abstract] [PDF]

				O. N. Nwasokwa, J. H. Koss, G. H. Friedman, A. M. Grunwald, and M. M. Bodenheimer Bypass Surgery for Chronic Stable Angina: Predictors of Survival Benefit and Strategy for Patient Selection Ann Intern Med, June 1, 1991; 114(12): 1035 - 1049. [Abstract] [PDF]

				G. S. Weinstein and B. Levin Crossovers in coronary artery bypass grafting trials Ann. Thorac. Surg., May 1, 1990; 49(5): 847 - 848. [PDF]

				L. D. Fisher, G. C. Kaiser, K. B. Davis, and M. B. Mock Reply Ann. Thorac. Surg., May 1, 1990; 49(5): 848 - 848. [PDF]

				L. D. Fisher, G. C. Kaiser, K. B. Davis, and M. B. Mock Crossovers in Coronary Artery Bypass Grafting Trials: Desirable, Undesirable, or Both? Ann. Thorac. Surg., October 1, 1989; 48(4): 465 - 466. [PDF]