A powerful experiment will have a high Signal/Noise ratio. Signal is the response to the treatment, noise is the within-group variation. Use of isogenic strains controls the noise by eliminating genetic variation. On average it does not alter the signal. In the simplest possible experiment two individuals which are as alike as possible are assigned at random either to a “treated” or a “control” group. Any difference between them is attributed to the effect of the treatment.
However no two individuals are exactly alike so it is necessary to use several animals in each group to average out any slight differences. The four experiments below explain the situation, assuming a measurement outcome
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Experiment 1
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Experiment 2
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Experiment 3
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Experiment 4
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