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Sample size considerations for superiority trials in systemic lupus erythematosus (SLE)

Department of Clinical Immunology and Allergy, Department of Medicine, The Montreal General Hospital, McGill University, Montreal, Quebec, Canada; The Montreal General Hospital, Division of Clinical Epidemiology, 1650 Cedar Avenue, Room L10-421, Montreal, Quebec, H3G 1A4, Canada; Tel: (+ 1) 514 934 4641; fax: (+ 1) 514 934 8293a

Lawrence Joseph

Division of Clinical Epidemiology, Department of Medicine, The Montreal General Hospital, McGill University, Montreal, Quebec, Canada; Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada

For reasons of efficiency and ethics, sample size calculations are an important part of the design of all clinical trials. This paper highlights the statistical issues inherent to the estimation of sample size requirements in superiority trials particular to SLE. Calculations based on statistical power for testing hypotheses have historically been the method of choice for sample size determination in clinical trials. The advantages of using confidence intervals (CI's) rather than P-values in reporting results of clinical trials is now well established. Since the design of a trial should match the analysis that will eventually be performed, sample size methods based on ensuring accurate estimation of important parameters via sufficiently narrow CI widths should be preferred to methods based on hypothesis testing. Methods and examples are given for sample size calculations for continuous and dichotomous outcomes from both a power and confidence interval width viewpoint. An understanding of sample size calculations in association with expert statistical consultation will result in better designed clinical trials that accurately estimate clinically relevant differences between treatment outcomes, thereby furthering the treatment of patients with SLE.

Key Words: systemic lupus erythematosus • sample size • clinical trials

Lupus, Vol. 8, No. 8, 612-619 (1999)
DOI: 10.1191/096120399680411326


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