title: Reducing sample sizes when comparing experimental and control groups.
abstract: 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: D012107:Research Design; D012494:Sampling Studies / Q000379:methods*