[R-meta] Meta-analysis per level or meta-regression

Just to add to this; these two pages on the metafor website are relevant
to this discussion:


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

https://www.metafor-project.org/doku.php/tips:different_tau2_across_subgroups

Best,
Wolfgang

-----Original Message-----
From: R-sig-meta-analysis [mailto:

r-sig-meta-analysis-bounces at r-project.org] On

Behalf Of James Pustejovsky via R-sig-meta-analysis
Sent: Monday, 20 March, 2023 19:27
To: R Special Interest Group for Meta-Analysis
Cc: James Pustejovsky
Subject: Re: [R-meta] Meta-analysis per level or meta-regression

Hi Catia,

I don't know of research that has looked at differences between these
approaches empirically.

I would interpret the issue in terms of a difference between two
meta-regression models: one in which the between-study heterogeneity is
constrained to be equal across levels of the moderator and one in which

the

between-study heterogeneity is allowed to differ by level of the

moderator.

Mar?a Rubio-Aparicio and colleagues compared these two models in a
simulation study:
https://doi.org/10.1080/00220973.2018.1561404

It's also now possible to fit and compare both models using metafor:
res_hom <- rma(yi, vi, mods = ~ alloc, data=dat)
res_het <- rma(yi, vi, mods = ~ alloc, scale = ~ alloc, data=dat)
anova(res_het, res_hom) # Likelihood ratio test and model fit statistics

Some analysts would simply fit both models and justify
their preferred model based on the fit statistics. Others might argue that
it's preferable to always use the more flexible model for purposes of
testing moderators; see Rodriguez et al. (2023;
https://doi.org/10.1111/bmsp.12299).

James

On Mon, Mar 20, 2023 at 1:04?PM Catia Oliveira via R-sig-meta-analysis <
r-sig-meta-analysis at r-project.org> wrote:

Dear all,

Does anyone know of a manuscript that has compared the effect sizes when
running separate meta-analyses per level of a variable of interest

against

those of running a meta-regression where we remove the intercept?

e.g.,

### mixed-effects meta-regression model with categorical moderator
res <- rma(yi, vi, mods = ~ alloc, data=dat)
res

You will find:

Test of Moderators (coefficients 2:3):
QM(df = 2) = 1.7675, p-val = 0.4132

Model Results:

                 estimate      se     zval    pval    ci.lb   ci.ub
intrcpt           -0.5180  0.4412  -1.1740  0.2404  -1.3827  0.3468
allocrandom       -0.4478  0.5158  -0.8682  0.3853  -1.4588  0.5632
allocsystematic    0.0890  0.5600   0.1590  0.8737  -1.0086  1.1867


Instead of doing this, we could also run one meta-analysis for

allocrandom

and another for allocsystematic.
I know the results will be similar, I just need to have something that
proves this beyond running the model and presenting the findings. Also,
meta-regression allows us to compare the different levels, which is the
point. I don't understand why we are questioned about this when running

a

meta-regression but if this was a linear regression using this approach
would be standard.

Best wishes,

Catia

--
C?tia Margarida Ferreira de Oliveira
Research Associate
Department of Psychology, Room C222
University of York, YO10 5DD
Twitter: @CatiaMOliveira
pronouns: she, her