# Power or Sample Size Calculator

Power analysis is an important aspect of experimental design. It refers to the probability that your test will find a statistically significant difference when such a difference actually exists. *Power* is the probability that you will reject the null hypothesis when you should (and thus avoid a Type II error). It is generally accepted that power should be 0.8 or greater; that is, you should have at least 80% chance of finding a statistically significant difference when there is one.

The following power or sample size calculators are for the statistical tests: