With no prior information, make an estimated guess on the effect size expected, or use an effect size that corresponds to the size of the effect ◦ Broad effect sizes categories are small, medium, and large ◦ Different statistical tests will have different values of effect size for each category □□□□□□ □□□□ ≈ □□□□1 −□□□□2 □□□. Use background information in the form of similar studies to get means and variation, then calculate effect size directly C. Use background information in the form of preliminary/trial data to get means and variation, then calculate effect size directly B. ![]() Given those three bits, and other information based on the specific design, you can calculate sample size for most statistical tests Effect Size in detail ◦ While Power and Significance level are usually set irrespective of the data, the effect size is a property of the sample data ◦ It is essentially a function of the difference between the means of the null and alternative hypotheses over the variation (standard deviation) in the data How to estimate Effect Size: A.The lower the significance level, the more likely it is to avoid a false positive and the more samples needed.AKA, probability of a Type I error (false positive).Standard setting for power is 0.80 Significance level (α): probability of falsely rejecting the null hypothesis even though it is true.The higher the power, the more likely it is to detect an effect if it is present and the more samples needed.Power = 1-β, where β is the probability of a Type II error (false negative).AKA, probability of detecting a true difference when it exists. ![]() ![]() The larger the effect size, the easier it is to detect an effect and require fewer samples Power: probability of correctly rejecting the null hypothesis if it is false.Mark Williamson, Statistician Biostatistics, Epidemiology, and Research Design Core DaCCoTA Purpose ◦ This Module was created to provide instruction and examples on sample size calculations for a variety of statistical tests on behalf of BERDC ◦ The software used is GPower, the premiere free software for sample size calculation that can be used in Mac or Windows Key Bits of Sample Size Calculation Effect size: magnitude of the effect under the alternative hypothesis Download Sample Size Calculation with GPower and more Medicine Exams in PDF only on Docsity!Sample Size Calculation with GPower Dr.
0 Comments
Leave a Reply. |