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Updated: Aug 9, 2026

Sampling Soils in a Heterogeneous Research Plot
Published on: January 7, 2019
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.
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