[R-meta] [R meta] How to print z score for subgroup analysis

[Cath Kids]

Dear Wolfgang,

Thank you so much for your detailed reply! The links are very helpful!

Regards,
Joanne

On Wed, May 22, 2019 at 9:32 AM Viechtbauer, Wolfgang (SP) <
wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:

> Dear Joanne,
>
> With "mixed-effects model for subgroup analysis", I assume you mean a
> meta-regression model with a categorical predictor and allowing for
> residual heterogeneity within subgroups. And I assume you are contrasting
> this with fitting random-effects models within each subgroup (so we get an
> estimate of mu_j for subgroups j = 1, ..., m) and then testing whether
> there are differences between subgroups (i.e., H_0: mu_1 = mu_2 = ... =
> mu_m). These two approaches are conceptually nearly identical, except that
> the mixed-effects meta-regression approach (usually) assumes that the
> amount of residual heterogeneity within subgroups (tau^2) is the same for
> all subgroups while the second approach allows the amount of heterogeneity
> within subgroups to differ across subgroups (so we get an estimate of
> tau^2_j for subgroup j). However, one can also fit a mixed-effects
> meta-regression model that allows tau^2 to differ across subgroups and then
> the two approaches are exactly identical. See:
>
> http://www.metafor-project.org/doku.php/tips:comp_two_independent_estimates
>
>
> For a further discussion/comparison of these two approaches (i.e.,
> assuming a single tau^2 vs. allowing different tau^2 values per subgroup),
> see the following article:
>
> https://www.tandfonline.com/doi/full/10.1080/00220973.2018.1561404
>
> Best,
> Wolfgang
>
> -----Original Message-----
> From: R-sig-meta-analysis [mailto:
> r-sig-meta-analysis-bounces using r-project.org] On Behalf Of Cath Kids
> Sent: Tuesday, 21 May, 2019 0:56
> To: Guido Schwarzer
> Cc: r-sig-meta-analysis using r-project.org
> Subject: Re: [R-meta] [R meta] How to print z score for subgroup analysis
>
> Dear Michael and Guido,
>
> Thank you very much for your reply!
> Yes, what I mean is z-scores for the individual subgroup effects. Thank you
> for the R command from Guido!
> I did report the between subgroup differences but I also see from the
> meta-analyses (at least those in my field) report each subgroup effect (z
> scores), so I thought I should report that too.
>
> I've got one more question, can anyone please enlighten me whether is it
> generally more preferable to use random-effect model for subgroup analysis
> than mixed effect model? (as suggested by Cochrane handbook
>
> https://handbook-5-1.cochrane.org/chapter_9/9_6_3_1_is_the_effect_different_in_different_subgroups.htm
> )
> Or is there any circumstance where it is better to use the mixed effect
> model? I read a few meta-analyses which used mixed effect model for
> subgroup analysis so I'm wondering why.
>
> Thank you very much!
>
> Regards,
> Joanne
>
> On Mon, May 20, 2019 at 10:21 AM Guido Schwarzer <sc using imbi.uni-freiburg.de>
> wrote:
>
> > Joanne,
> >
> > The z-scores for the individual subgroup effects (if this is what you
> > are looking for) are not shown in the output, however, they are part of
> > the meta-analysis object.
> >
> > You can use the following command to extract the z-scores and p-values
> > for the fixed effect and random effects model:
> >
> > with(post_cb2_es.subgroup,
> >       data.frame(bylevs, zval.fixed.w, pval.fixed.w,
> >                  zval.random.w, pval.random.w))
> >
> > However, you should abstain from selectively reporting significant
> > subgroup results. Instead, the Cochrane Handbook
> > (https://handbook-5-1.cochrane.org/) gives the following advice (among
> > other things) on subgroup analyses: (1) conduct a test for subgroup
> > differences (section 9.6.3.1) which Michael already mentioned and (2) do
> > not compare the statistical significance of the results within separate
> > subgroup analyses (section 9.6.6).
> >
> > Best wishes, Guido
> >
> > --
> > Dr. Guido Schwarzer
> > Institute of Medical Biometry and Statistics,
> > Faculty of Medicine and Medical Center - University of Freiburg
> >
> > Postal address: Stefan-Meier-Str. 26, D-79104 Freiburg
> >
> > Phone: +49/761/203-6668
> > Mail: sc using imbi.uni-freiburg.de
> > Homepage: http://www.imbi.uni-freiburg.de
>

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