[R-meta] Difference of difference

[Viechtbauer, Wolfgang (SP)]

Start by reading:

https://wviechtb.github.io/metafor/reference/anova.rma.html
https://wviechtb.github.io/metafor/reference/predict.rma.html

And lots of examples here:

https://www.metafor-project.org/doku.php/tips:testing_factors_lincoms
https://www.metafor-project.org/doku.php/tips:multiple_factors_interactions

And here:

https://www.metafor-project.org/doku.php/tips:models_with_or_without_intercept

Best,
Wolfgang

>-----Original Message-----
>From: Stefanou Revesz [mailto:stefanourevesz using gmail.com]
>Sent: Sunday, 30 January, 2022 5:18
>To: Viechtbauer, Wolfgang (SP)
>Cc: R meta
>Subject: Re: Difference of difference
>
>Thank you so much, Wolfgang. I must admit that I failed at achieving
>this on my own. In my model below, I want to test:
>(coef 4 - coef 1) - (coef 5 - coef 2)
>
>Would that be possible either in anova.rma() or in clubSandwich::Wald_test()?
>
>dd <- read.csv("https://raw.githubusercontent.com/fpqq/w/main/1.csv")
>dd$obs <- 1:nrow(dd)
>
>res <- rma.mv(gi ~ 0 + teaching_level:time, vi, random = ~1|study/obs,
>data = dd)
>
>Many thanks,
>Stefanou
>
>On Fri, Jan 28, 2022 at 9:54 AM Viechtbauer, Wolfgang (SP)
><wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:
>>
>> 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