| 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. |
