The Sample Size windows and computations to test sample sizes and power for proportions are similar to those for testing means. You enter a true Proportion and choose an Alpha level. Then, for the onesample proportion case, enter the Sample Size and Null Proportion to obtain the Power. Or, enter the Power and Null Proportion to obtain the Sample Size. Similarly, to obtain a value for Null Proportion, enter values for Sample Size and Power. For the twosample proportion case, either the two sample sizes or the desired Power must be entered. (See Power and Sample Window for OneSample Proportions and Difference Between Two Proportions for a TwoSided Test.)
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