# [R-meta] ANALYSIS OF SUBGROUPS WITH DIFFERENT MODELS OF EFFECTS IN EACH SUBGROUP

James Pustejovsky jepu@to @end|ng |rom gm@||@com
Fri Aug 26 16:26:59 CEST 2022

```Hi all,

Please see below for a message from Wolfgang, who is still experiencing
technical difficulties with the listserv.

James

---------------------------------------------------------------------------------------------------------------------------------------------------

Dear Lorenzo,

One can fit a single model that allows tau^2 and the mean effects to differ
across subgroups as described here:

https://www.metafor-project.org/doku.php/tips:comp_two_independent_estimates#meta-regression_with_all_studies_but_different_amounts_of_residual_heterogeneity

This is identical to fitting random-effects models in each subgroup. One
could of course also fit an equal-effects model within a particular
subgroup. This is identical to fixing the tau^2 value to 0 for that
subgroup. For example, here I fix the tau^2 value for the 'alternate' level
to 0 (which is like imposing an equal-effects model on this subgroup):

dat <- escalc(measure="RR", ai=tpos, bi=tneg, ci=cpos, di=cneg,
data=dat.bcg) res <- rma.mv(yi, vi, mods = ~ 0 + alloc, random = ~ alloc |
trial,

struct="DIAG", data=dat, digits=3, tau2=c(0,NA,NA))

If one wants an overall mean (this is what I think you mean by "final
summary"), then I would suggest to compute an adjusted/marginal mean:

So, something like:

predict(res, newmods = colMeans(model.matrix(res)))

or

predict(res, newmods = c(1/3, 1/3, 1/3))

depending on the type of population to which this overall mean is supposed
to refer to.

Best,

Wolfgang

On Sun, Aug 21, 2022 at 12:17 AM Martin Lobo <mlobo4370 using hotmail.com> wrote:

>
> Hi every one,
> I have a doubt with the subgroup analysis. in some cases the heterogeneity
> of each group is different, being able to use a fixed effect model and in
> other occasions one of random effects. Can this be done in the subgroup
> analysis, choosing one model for each subgroup and another for the final
> summary?
>
> Thank's
>
>
>
> Lorenzo Martín Lobo MTSAC, FACC, FESC
> Jefe de Dpto Enf. Cardiovasculares y Cardiometabolismo Hospital Militar
> Campo de Mayo.
> Jefe de Cardiología Hospital Militar Campo de Mayo
> Ex Jefe de Unidad Coronaria Hospital Militar Campo de Mayo
> Miembro Titular de la Sociedad Argentina de Cardiología
> Fellow American College of Cardiology
> Fellow European Society of Cardiology
> Ex Miembro del Area de Investigación de la SAC
> Ex Director del Consejo de Aterosclerosis y Trombosis de la SAC
> Miembro Asesor del Consejo de Aterosclerosis y Trombosis de la SAC
> Ex Director del Consejo de Epidemiología y Prevención Cardiovascular de la
> SAC
>
> Miembro Asesor del Consejo de Epidemiología y Prevención Cardiovascular de
> la SAC
>
>
> Experto en Lipidos de la Sociedad Argentina de Lipidos.
> Miembro de la Sociedad Argentina de Lipidos.
> Instructor de ACLS de la American Heart Association
>
>
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>
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