Power analysis for comparing 2 ratios
If you have 2 different groups and are going to compare the rates obtained from these groups, you can estimate the minimum number of participants required in each group using the rates you determined from the literature.
Required information
α error: shows the significance level of the p value. Choose between 0.05 and 0.01.
Strength (1-β): Select between 80% and 90% for targeted strength
Expected rate in group I:
Expected rate in group II:
Sample calculation: In order to find a significant difference between the groups at the 0.05 level and with 80% power when one of the expected rates in two groups is 20% and the other is 60%, the information should be entered into the application as follows to calculate the minimum number of participants required in each group.
After checking Calculate, you can reach the minimum number of patients required. This field can be copied.
Referans: Wang, H. and Chow, S.-C. 2007. Sample Size calculation for Comparing Proportions. (pages 3-4; section3.1 Test for Equality).Wiley Encyclopedia of ClinicalTrials.