P.Mean: Power calculations for repeated measures designs (created 2008-09-25).

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I’ve been struggling with a design/analysis question related to repeated measures design and power analysis. Can you help?

This is a very general question, and specific answers will vary depending on the specific context of the problem. Here's a very vague answer to give you an idea of what you need to worry about.

Power calculations for repeated measures designs usually requires an extra piece of information. Rather than a single standard deviation, you need to specify a between subject standard deviation and a within subject standard deviation. Alternately, you could provide information about the total standard deviation (both between and within variation) and then a within subject correlation. Finally, you can simplify many repeated measures designs by looking at a change score. If there are more than two repeated measures, then often the change score between the first time point and the last time point is useful.

This work is licensed under a Creative Commons Attribution 3.0 United States License. This page was written by Steve Simon and was last modified on 2010-04-01. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Category: Sample size justification.