Alpha values as a function of sample size, effect size, and power: accuracy over inference.
Tables of alpha values as a function of sample size, effect size, and desired power were presented. The tables indicated expected alphas for small, medium, and large effect sizes given a variety of sample sizes. It was evident that sample sizes for most psychological studies are adequate for large effect sizes defined at .8. The typical alpha level of .05 and desired power of 90% can be achieved with 70 participants in two groups. It was perhaps doubtful if these ideal levels of alpha and power have generally been achieved for medium effect sizes in actual research, since 170 participants would be required. Small effect sizes have rarely been tested with an adequate number of participants or power. Implications were discussed.
Department of Psychology, University of New Brunswick, P.O. Box 5050, Tucker Park Road, Saint John, NB, Canada E2L 4L5. Bradley@UNB.ca
M T
MT
Bradley
A
A
Brand
D003627:Data Interpretation, Statistical; D006801:Humans; D011584:Psychology / Q000379:methods* / Q000592:standards; D012107:Research Design / Q000706:statistics & numerical data*; D018401:Sample Size