Reducing sample sizes when comparing experimental and control groups

Arch Environ Health. May-Jun 1976;31(3):169-70. doi: 10.1080/00039896.1976.10667213.


In comparing rates for two groups (one control and the other experimental), one may use an historical control to reduce the sample size needed for a test of significance to one-fourth that required if the control is not historical. If there is some doubt as to whether one's control is comparable to the historical control, a test showing the equality of the historical and experimental controls can lead to a halving of the sample required for significance testing. This same argument also applies to the comparison of two means.

MeSH terms

  • Research Design*
  • Sampling Studies / methods*