## Sample Size and Power Analysis

Each of these four components of your study (sample size, statistical power, effect size, and significance level) are a function of the other three, meaning that altering one causes changes in the others.

**Sample size** is critical to ensuring the validity of your study and should be determined in the very early stages of study design The effect size of your study is critical; this unique measurement will tell you the strength or importance of a particular relationship.

**Power** is the measurement of the probability of committing a Type II error, which is the probability of not finding a relationship that exists in your analysis. The a priori power is unique to every study.

The alpha or significance level of your study is the probability of committing a Type I error. More simply, it is the probability of finding a relationship that does not exist. Generally, committing a Type I error is considered more severe than committing a Type II error.

The significance level measurement is unique to your study. The significance level for a study involving airbag deployment failures would not be the same as the significance level for a study involving the satisfaction of five-year-old children with a particular brand of red crayon.

via Sample Size and Power Analysis | Statistics Solutions.

**Getting the Sample Size Right: A Brief Introduction to Power Analysis **Link