Setting an Optimal α That Minimizes Errors in Null Hypothesis Significance Tests
Figure 2
Determination of optimal α from the a priori combined probabilities of Type I and Type II error.
α and ω (the average of Type I and Type II error) for independent, 2-tailed, 2-sample t-tests (n1 = n2). Data are for 3 (dotted line), 10 (solid line), and 30 (double line) samples per group, with critical effect sizes of 1 SD of either group. Drop lines indicate the minimum average of Type I and Type II error and its associated value of α.