In a recent post, I discussed the differences between repeated measures and longitudinal data, and some of the issues that come up in each one.
I want to expand on that discussion, and discuss the three approaches you can take to analyze repeated measures data.
For a few, very specific designs, you can get the exact same results from all three approaches. This, I find, has always made it difficult to figure out what each one is doing, and how to apply them to OTHER designs.
For the purposes of discussion here, I’m going to define repeated measures data as repeated measurements of the same outcome variable on the same individual. The individual is often a person, but could just as easily be a plant, animal, colony, company, etc. For simplicity, I’ll use “individual.” (more…)