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. 1988 Sep 10;297(6649):672–676. doi: 10.1136/bmj.297.6649.672

Graphical aid for determining power of clinical trials involving two groups.

D K Miller 1, S M Homan 1
PMCID: PMC1834346  PMID: 3179550

Abstract

Physicians need to evaluate clinical research critically, and determining the power of a study is an essential component of research evaluation. This report presents a graphical aid that permits rapid power determination for clinical trials with two groups. Power curves were developed for dichotomous outcomes by setting two tail alpha at 0.05 and varying the sample size, the control group response rate, and the clinically important difference between control and experimental groups as defined by the user. Use of the graphical aid was demonstrated to a group of 18 medical students, residents, fellows, and faculty in a 15 minute session. Evaluation of the trainees' application of the aid showed a small average bias of -0.0003 and an average variance of 0.006. Ninety percent of power estimates were within 0.05 of the true value determined by formula. This graphical aid is recommended as a rapid and accurate method for determining power in the critical appraisal of clinical research.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Altman D. G. Statistics and ethics in medical research: III How large a sample? Br Med J. 1980 Nov 15;281(6251):1336–1338. doi: 10.1136/bmj.281.6251.1336. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Bennett K. J., Sackett D. L., Haynes R. B., Neufeld V. R., Tugwell P., Roberts R. A controlled trial of teaching critical appraisal of the clinical literature to medical students. JAMA. 1987 May 8;257(18):2451–2454. [PubMed] [Google Scholar]
  3. Browner W. S., Newman T. B. Are all significant P values created equal? The analogy between diagnostic tests and clinical research. JAMA. 1987 May 8;257(18):2459–2463. [PubMed] [Google Scholar]
  4. DerSimonian R., Charette L. J., McPeek B., Mosteller F. Reporting on methods in clinical trials. N Engl J Med. 1982 Jun 3;306(22):1332–1337. doi: 10.1056/NEJM198206033062204. [DOI] [PubMed] [Google Scholar]
  5. Detsky A. S., Sackett D. L. When was a "negative" clinical trial big enough? How many patients you needed depends on what you found. Arch Intern Med. 1985 Apr;145(4):709–712. [PubMed] [Google Scholar]
  6. Dyken M. L. Transient ischemic attacks and aspirin, stroke and death; negative studies and Type II error. Stroke. 1983 Jan-Feb;14(1):2–4. doi: 10.1161/01.str.14.1.2. [DOI] [PubMed] [Google Scholar]
  7. Emerson J. D., Colditz G. A. Use of statistical analysis in the New England Journal of Medicine. N Engl J Med. 1983 Sep 22;309(12):709–713. doi: 10.1056/NEJM198309223091206. [DOI] [PubMed] [Google Scholar]
  8. Feigl P. A graphical aid for determining sample size when comparing two independent proportions. Biometrics. 1978 Mar;34(1):111–122. [PubMed] [Google Scholar]
  9. Freiman J. A., Chalmers T. C., Smith H., Jr, Kuebler R. R. The importance of beta, the type II error and sample size in the design and interpretation of the randomized control trial. Survey of 71 "negative" trials. N Engl J Med. 1978 Sep 28;299(13):690–694. doi: 10.1056/NEJM197809282991304. [DOI] [PubMed] [Google Scholar]
  10. Gardner M. J., Altman D. G. Confidence intervals rather than P values: estimation rather than hypothesis testing. Br Med J (Clin Res Ed) 1986 Mar 15;292(6522):746–750. doi: 10.1136/bmj.292.6522.746. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Lachin J. M. Introduction to sample size determination and power analysis for clinical trials. Control Clin Trials. 1981 Jun;2(2):93–113. doi: 10.1016/0197-2456(81)90001-5. [DOI] [PubMed] [Google Scholar]
  12. Landecker K. D., McCallum E. M., Fevre D. I., Green R., Kasumi A., Piper D. W. Effect of sodium amylosulfate (Depepsen) on the healing of duodenal ulcer. Gastroenterology. 1976 Nov;71(5):723–725. [PubMed] [Google Scholar]
  13. Reed J. F., 3rd, Slaichert W. Statistical proof in inconclusive 'negative' trials. Arch Intern Med. 1981 Sep;141(10):1307–1310. [PubMed] [Google Scholar]
  14. Relman A. S. A new series on biostatistics. N Engl J Med. 1982 Jun 3;306(22):1360–1361. doi: 10.1056/NEJM198206033062212. [DOI] [PubMed] [Google Scholar]
  15. Simon R. Confidence intervals for reporting results of clinical trials. Ann Intern Med. 1986 Sep;105(3):429–435. doi: 10.7326/0003-4819-105-3-429. [DOI] [PubMed] [Google Scholar]
  16. Simoons M. L., Arnold A. E., Betriu A., de Bono D. P., Col J., Dougherty F. C., von Essen R., Lambertz H., Lubsen J., Meier B. Thrombolysis with tissue plasminogen activator in acute myocardial infarction: no additional benefit from immediate percutaneous coronary angioplasty. Lancet. 1988 Jan 30;1(8579):197–203. doi: 10.1016/s0140-6736(88)91062-8. [DOI] [PubMed] [Google Scholar]
  17. Sorensen P. S., Pedersen H., Marquardsen J., Petersson H., Heltberg A., Simonsen N., Munck O., Andersen L. A. Acetylsalicylic acid in the prevention of stroke in patients with reversible cerebral ischemic attacks. A Danish cooperative study. Stroke. 1983 Jan-Feb;14(1):15–22. [PubMed] [Google Scholar]
  18. Young M. J., Bresnitz E. A., Strom B. L. Sample size nomograms for interpreting negative clinical studies. Ann Intern Med. 1983 Aug;99(2):248–251. doi: 10.7326/0003-4819-99-2-248. [DOI] [PubMed] [Google Scholar]

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