Effect Size In Sample Size Calculation. One-tailed t-test with two independent groups of equal size small effect size see Piasta SB. Sample size calculator When preparing to conduct a trial you will want to make sure that the experiment has sufficient statistical power.
In making the calculation you want you need one of the numbers. Having these values gives you the required n. For a 2 x 2 chi-square analysis phi is often used.
Generally effect size is calculated by taking the difference between the two groups eg the mean of treatment group minus the mean of the control group and dividing it by the standard deviation of one of the groups.
There are different effect size statistics for different types of analyses. First using the T statistic with a non-centrality parameter then using the Z statistic. Use the compromise function to compute alpha and beta for a sample half. One-tailed t-test with two independent groups of equal size small effect size see Piasta SB.
