One-Sample and Two-Sample Proportions | JMP 13.2

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Design of Experiments Guide • Prospective Sample Size and Power • One-Sample and Two-Sample Proportions

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One-Sample and Two-Sample Proportions

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 one-sample 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 two-sample proportion case, either the two sample sizes or the desired Power must be entered. (See Power and Sample Window for One-Sample Proportions and Difference Between Two Proportions for a Two-Sided Test.)

The computations to determine sample size and null proportions use exact methods based on the binomial distribution. Such methods are more reliable than using the normal approximation to the binomial, which can provide erroneous results for small samples or proportions close to 0 or 1.

For a single proportion, results are based on exact power calculations used in conjunction with one of the following:

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The “Add two successes and two failures” adjusted Wald test statistic described in Agresti and Coull (1998). See also Section 3.3 in the white paper by Barker on the JMP website: http://www.jmp.com/en_us/whitepapers/jmp/power-sample-calculations.html

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The Clopper-Pearson exact confidence interval method (Clopper and Pearson, 1934; Agresti and Coull, 1998, Section 1)

For two proportions, results are based on exact power calculations for the adjusted Wald statistic proposed by Agresti and Caffo (2000).

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Help created on 9/19/2017