Power Calculation

A power calculation is a necessary step for any research project and is required for almost all grant applications. The purpose of a power calculation is to determine an estimate of how many participants or observations are required in order to generate statistically significant results. There are three aspects which are used in deriving your power calculation.

Power Calculation Information

The research design is built around testing the research hypothesis. While this does not empirically determine your sample size requirements, it provides the road map to how your research is structured. Differences in research design, such as having two or three groups, will change the number of participants needed.

The greater the expected variability in your outcome measure, the fewer participants you will need. You can base your estimate of the variability on past studies that are similar to the one you want to conduct. If you are breaking new ground and do not have a literature review on which to make an estimate, you can run a pilot study when appropriate.

You will also need to know how big of a change you are looking for. Because variability occurs in nature, you need to be looking for a measured change that is larger than would occur by chance. Try to figure out what percent of change would produce the result that you are looking for.