American Journal of Epidemiology 2005 161(2):105-110; doi:10.1093/aje/kwi014
Copyright © 2005 by the Johns Hopkins Bloomberg School of Public Health
SPECIAL ARTICLE |
Ethics and Sample Size
1 Division of Biostatistics, Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco, CA.
2 Program in Medical Ethics, Department of Medicine, School of Medicine, University of California, San Francisco, CA.
The belief is widespread that studies are unethical if their sample size is not large enough to ensure adequate power. The authors examine how sample size influences the balance that determines the ethical acceptability of a study: the balance between the burdens that participants accept and the clinical or scientific value that a study can be expected to produce. The average projected burden per participant remains constant as the sample size increases, but the projected study value does not increase as rapidly as the sample size if it is assumed to be proportional to power or inversely proportional to confidence interval width. This implies that the value per participant declines as the sample size increases and that smaller studies therefore have more favorable ratios of projected value to participant burden. The ethical treatment of study participants therefore does not require consideration of whether study power is less than the conventional goal of 80% or 90%. Lower power does not make a study unethical. The analysis addresses only ethical acceptability, not optimality; large studies may be desirable for other than ethical reasons.
ethics committees; ethics, research; sample size
Correspondence to Dr. Peter Bacchetti, Box 0560, University of California, San Francisco, CA 94143-0560 (e-mail: peter{at}biostat.ucsf.edu).
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