Search tips
Search criteria 


Logo of bmjLink to Publisher's site
BMJ. 1989 September 9; 299(6700): 663–665.
PMCID: PMC1837599

Sample size and power for comparing two or more treatment groups in clinical trials.


Methods for determining sample size and power when comparing two groups in clinical trials are widely available. Studies comparing three or more treatments are not uncommon but are more difficult to analyse. A linear nomogram was devised to help calculate the sample size required when comparing up to five parallel groups. It may also be used retrospectively to determine the power of a study of given sample size. In two worked examples the nomogram was efficient. Although the nomogram offers only 5% and 1% significance levels and can be used only for up to five treatment groups, this is sufficient for most researchers.

Full text

Full text is available as a scanned copy of the original print version. Get a printable copy (PDF file) of the complete article (599K), or click on a page image below to browse page by page.

Articles from BMJ : British Medical Journal are provided here courtesy of BMJ Group