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Analyzing Repeated Measures Data in JMP® Software - masterthesis example

ThomasVH

Hi,

I was wondering if someone could verify if I took the right steps in setting up a mixed model for repeated measures for the following research:

In our research we had 2 groups of soccer players (amateur vs. professionals).

Each player of both groups performed 3 physical tests (a short vs. a long laboratory test vs. a field test), each test was performed on different days.Our outcome measure was VO2max (physical capacity).

Purpose: I mainly want to compare the VO2max between the amateur vs. professionals for each physical test. (2x3 table)

So I thought I should use a 2-way repeated measure ANOVA. In JMP pro 12-> a mixed model repeated measures.

But i'm not sure about which factor I should put in the fixed effect and/or random effect box when using Analyse -> fit model for my purpose.

Can someone please verify if I did the right thing in the two last pictures below? (The first picture is just a small selection from my data.)

Kind regards,

Thomas

Accepted answers

Mark_Bailey

I conferred with my colleagues who are wiser, smarter, and much better looking than me. They suggest that you should not estimate the interaction term as I suggested. It will confound subject with the residual as I discovered.

So go back to the beginning and your original mixed model seems like the way to go after all.Specifically, start a mixed model including the two main fixed effects and the random subject effect. Indicate nesting of subject within the other two factors. That specification should do it.

All comments

Mark_Bailey

I don't think that this study requires a repeated measures analysis. It appears to simply be a two-way ANOVA:

V(O2max) = Intercept + Level + Physical Test + Level * Physical Test. The subject is your residual, so you do not need to enter an explicit term to estimate it. The factor levels are crossed, not nested in this case.

You should be able to use the Standard Least Squares personality in this case.

ThomasVH

Hi Mark,

Thank you for your answer.

The reason why I thought to use a mixed model instead of a 2-way ANOVA is the fact the VO2max values are based on repeated measures. For instance, subject 1 did three tests a short one (64,6 VO2max), the week after a long one (54,7 VO2max), again one week later a field test (52,86 VO2max). The same is for the other subjects.

Does this justify the use of the mixed model?

If it justifies the mixed model. Should I leave the random effect box empty like you suggest? Or fill in the subject factor in the random effect box?

Thanks in advance.

Kind regards,

Thomas

Mark_Bailey

I see your point. Subject is a blocking structure and its effect is random. I think that it makes sense to include it as a random effect after all.

I still don;t see this study as an example of 'repeated measures' but my definition might be too strict. It is just a two-way ANOVA with blocking.

Consider including the interaction term as I think it is estimabile and, if so, could be informative.

ThomasVH

I'm a little confused now. Perhaps I should clarify the whole study better.

We tested lots of players. Some of these players were professional and others were amateurs. But we tested them in group. For instance week 1 on monday each amateur did 1 test, the same week on tuesday each professional did 1 test. In week 2 on monday each amateur did another test, the same week on tuesday each professional did another test. Finally, in week 3 each amateur did a third test on monday and each professional did his third test on tuesday.

Now we want to test if the VO2max differs between the level (prof vs. amateur) with taking the different type of physical test (short vs. long vs. field) into account.

Taking your previous answers into account I think my analyse + data should look like this. I have also add the future 2x3 table I want to solve (I tried it once).

Do I still have to use just a 2-Way ANOVA?

Kind regards,