Computes the sample size in each group (assuming equal sample sizes) required to perform an equivalence test for the difference in population proportions with desired power in a 2-group design. The value of h specifies a range of practical equivalence, -h to h, for the difference in population proportions. The absolute difference in the proportion planning values must be less than h. Equivalence tests often require a very large sample size. Equivalence tests usually use 2 x alpha rather than alpha (e.g., use alpha = .10 rather than alpha = .05). This function sets the effect size equal to the difference in proportion planning values.