# Sample Size / Power Analysis

Every study needs data, the question is how much data are needed. The sample size determination using a power analysis is the process of figuring that question out and will be of particular interest to both your committee for Proposal and IRB approval. Details below briefly examine how a power analysis calculates sample size, before going into how to use free resources to determine your study’s sample size in just a few minutes.

** Power Analysis.** For a given statistical test, the sample size is calculated from statistical power, effect size, and significance level. That is, each of these four components of your study—namely, sample size, statistical power, effect size, and significance level—are a function of the other three. Specifically, the effect size of your study tells you the strength or importance of a particular relationship. The power, typically .80, is the probability of not making a type II error, which differs from beta, or the probability of making a type II error. The

** Free Resources.** To facilitate sample size determination, our team has calculated the sample size for a large variety of statistical tests for small, medium and large effect sizes. You can simply sign-up for the toolbox, then click the analysis you plan on using.

If you have trouble with the toolbox or would like more assistance, you can contact us for a free dissertation consultation. For additional assistance with your proposal, call (877-437-8622) or email us at [email protected].