Sample Size calculators
The calculator determines the sample size to gain the required test power and draw the power analysis chart.
Larger sample size increases the statistical power.
Researchers usually use the power of 0.8 which mean the probability of type II error (β), failure to reject an incorrect H0.2, is 0.2. The commonly used significant level (α) is 0.05. β is usually four times bigger than α, since rejecting a correct null assumption consider to be more severe than failing to reject a correct invalid assumption.