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  A-priori Sample Size Calculator for Student's t-Test

This calculator will tell you the minimum required total sample size and per-group sample size for a one-tailed or two-tailed t-test study, given the alpha level, the anticipated effect size, and the desired statistical power level.

Please supply the necessary parameters, and then click the 'Calculate' button.

Alpha Level: Also known as the p-value, probability, or type I error rate. By convention, this value should be less than or equal to 0.05 to claim statistical significance.
Anticipated Effect Size (Cohen's d): By convention, effect sizes of 0.2, 0.5, and 0.8 are considered small, medium, and large, respectively. To compute an effect size from group means and standard deviations, click here.
Desired Statistical Power Level: By convention, this value should be greater than or equal to 0.80.

 
 
 
 
The Statistics Calculators index now contains 56 free statistics calculators.

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