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Approximate Sample Size Calculator:
Comparing Two Means

The expected difference between two means is and the common within group standard deviation is . The per group sample size that gives an 80 chance that an 0.05 level test of significance will find a statistically significant difference between two sample means are compared is approximately .

When three means are compared, the approximate per group sample size adjusting for multiple comparisons is .

When four means are compared, the approximate per group sample size adjusting for multiple comparisons is observations per group.


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