[SOLVED] anova repeated measures - post hoc problems

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pedrak
Posts: 16
Joined: Tue Apr 11, 2017 7:54 am

[SOLVED] anova repeated measures - post hoc problems

Post by pedrak »

Dear Friends,
I have just performed a repeated measures anova (T0, T1, T2) and asked for a post hoc analysis.
Something went wrong in the post hoc, all "SE" were reported with the same value.
Just because it looked strange to me I performed the same analysis with Jasp and R. The results were different .
RM.PNG
RM.PNG (32.95 KiB) Viewed 4513 times
Please find attached a screenshot of the results and the file with the data.

Very best regards
Giuseppe
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Ravi
Posts: 194
Joined: Sat Jan 28, 2017 11:18 am

Re: anova repeated measures - post hoc problems

Post by Ravi »

Hi Giuseppe,

How did you calculate the post-hoc tests in R? We use lsmeans to calculate the post-hoc tests which uses the pooled variance from all groups that are being compared. Therefore, all standard errors have the same value. Using the pooled variance has some benefits such as a higher power, and it's a bit more robust when there are only a few counts in certain cells. I think JASP is just doing multiple t-tests and thus is using the variance of the difference between the two groups that are being compared.

Cheers,
Ravi
pedrak
Posts: 16
Joined: Tue Apr 11, 2017 7:54 am

Re: anova repeated measures - post hoc problems

Post by pedrak »

Hi Ravi,

many thanks for your clear reply, I apologize for thinking it was a mistake. Generally I use the multcomp package in R, but i must confess that for the example above I used R Commander with some of the Rcmdr plugins. The post hoc test are indeed based on multiple t-test with the bonferroni correction.
Thanks again for your time.

Cheers,
Giuseppe
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Ravi
Posts: 194
Joined: Sat Jan 28, 2017 11:18 am

Re: anova repeated measures - post hoc problems

Post by Ravi »

No problem, happy to help :slightly_smiling_face:
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