A power analysis is a calculation that helps you determine a minimum sample size for your study. It’s made up of four main components. If you know or have estimates for any three of these, you can calculate the fourth component.
Statistical power: the likelihood that a test will detect an effect of a certain size if there is one, usually set at 80% or higher.
Sample size: the minimum number of observations needed to observe an effect of a certain size with a given power level.
Significance level (alpha): the maximum risk of rejecting a true null hypothesis that you are willing to take, usually set at 5%.
Expected effect size: a standardized way of expressing the magnitude of the expected result of your study, usually based on similar studies or a pilot study.