[R-meta] Difference of difference

[Viechtbauer, Wolfgang (SP)]

Hi Stefanou,

It's certainly something you can do.

anova() can provide a test of such a contrast and predict() will give you the CI.

Best,
Wolfgang

>-----Original Message-----
>From: Stefanou Revesz [mailto:stefanourevesz using gmail.com]
>Sent: Thursday, 27 January, 2022 22:37
>To: R meta
>Cc: Viechtbauer, Wolfgang (SP)
>Subject: Difference of difference
>
>Dear Wolfang and the list Members,
>
>I've done a post-hoc after my 3-level model. Below is part of the results.
>
>At Baseline, elementary was larger than the mixed group by .251 (ignore pval).
>
>At post-test1, elementary was larger than the mixed group by .467 (ignore pval).
>
>Shall we again subtract the baseline difference from the post-test1
>difference to better understand the difference between mixed and
>elementary groups at post-test1?
>
>If yes, can we then conduct a test on that difference and get CIs for it?
>
>
>Diff       SE       tval   Df   pval
>mixed Baseline - elementary Baseline      -0.251   0.277  -0.905   55 0.984
>mixed Post-test1 - elementary Post-test1  -0.467   0.251  -1.861   55 0.582
>
>Thank you so much,
>Stefanou