Calculation for power analysis:

t-tests—Means: Difference between two independent means (two groups) Analysis: A priori: Compute required sample size Input:    Tail(s) = Two  Effect size d = 1.2041300  α err prob = 0.05  Power (1-β err prob) = 0.95  Allocation ratio N2/N1 = 1 Output: Noncentrality parameter δ = 3.7113779  Critical t = 2.0280940  Df = 36 Sample size group 1 = 19  Sample size group 2 = 19  Total sample size = 38  Actual power = 0.9506005