[R-meta] Subgroup analyses under the multi-level (3 level) meta-analysis model

[Viechtbauer, Wolfgang (SP)]

Dear Saya,

You do not need to create these 'dummy variables' yourself. Just declare the variable that distinguishes the various subgroups as a factor and include it as a predictor via 'mods'. You also might want to read this:

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

It's not focused on rma.mv() (i.e., it uses a simpler model), but the same principles apply.

Best,
Wolfgang

>-----Original Message-----
>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On
>Behalf Of Saya Fujita
>Sent: Sunday, 14 March, 2021 16:24
>To: R-sig-meta-analysis using r-project.org
>Subject: [R-meta] Subgroup analyses under the multi-level (3 level) meta-analysis
>model
>
>Dear All,
>
>I am conducting a 3-level multi-analysis, following this Bookdown.
>https://bookdown.org/MathiasHarrer/Doing_Meta_Analysis_in_R/mlma.html
>
>I would like to run some sub-group analyses under this 3 level structure, and I
>can see in this bookdown (chapter 12.1) that if I use rma.mv function in metafor,
>we need to create two variables/columns for each subgroup level. In the example in
>this book down, the number of sub-groups was two: peer-review, dissertation, so it
>makes sense that they coded 1 (yes) or 0 (no).
>
>In my data I have more than two subgroups, and I wonder how I should input the
>data. I thought, if I have 4 subgroups for instance, I’d create 4 columns and code
>0 or 1 in each column, but that would group 3 different levels as 0 in one column,
>and specifying one variable/column as a moderator in rma.mv using
>the mods parameter would compare one subgroup with the other three subgroups –
>which is not what I want to do. Hope this makes sense!
>I wonder if anyone here has done a subgroup analysis for multiple subgroup
>comparisons, maintaining the 3 level structure of a multi-level meta-analysis?
>Could I ask how you did the analysis?
>
>Thank you very much in advance, and I apologise if it’s a very simple/naïve
>question!
>
>Many thanks,
>Saya
>
>*********
>Sayaka Kidby (Fujita)| PhD candidate, Marie Skłodowska-Curie Early Career
>Researcher [she/her]
>Psychology | Lancaster University
>s.kidby using lancaster.ac.uk
>www.lancaster.ac.uk