Specify the population characteristics:

\(H_0: \mu_{1} - \mu_{2} = \)
\(H_a: \mu_{a1} -\mu_{a2}=\)
\(\sigma_1 =\)
\(\sigma_2 =\)
Or enter a standardized effect size
\( \frac{\left(\mu_{a1} - \mu_{a2}\right) - \left(\mu_{1} -\mu_{2}\right)}{\sigma} = \delta = \)

Specify the properties of the test:

Type of test	Two-tails Positive one-tail Negative one-tail
Type I error rate, \(\alpha =\)
Power=
Sample size for group 1, \(n_1=\)
Sample size for group 2, \(n_2=\)

Provide the population characteristics by entering the difference of means and standard deviation of each population. If the standard deviations are the same value, the program will compute the standardized effect size.

Alternatively, enter the standardized effect size, and the means and standard deviations will be filled with one possible set of values.

Select the type of test and the Type I error rate. Enter either a desired power value or a sample size and click the corresponding button to either Calculate minimum sample size or Calculate power .

The calculator automatically uses the standard \(t\) test when the sample sizes are equal or the standard deviations are equal. It uses Welch's test when the sample sizes and standard deviations are unequal.

When computing the minimum sample size to achieve a desired power, the program assumes that \(n_1=n_2\), and thus uses the standard \(t\) test for the calculations.