Determining the appropriate sample size is of great importance. Too small and important effects may be missed. Too large and the experiment will waste time, scientific resource and animals. Unfortunately, there is no perfect method, but the Power Analysis and the Resource Equation methods which are, in many ways, complementary are better than subjective judgement. Three methods for determining sample size are discussed here.
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Previous experience or custom
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Power analysis
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The “Resource equation” method
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