[R-meta] Questions about Omnibus tests

[Rafael Rios]

Dear Wolfgang,

Thank you for the clarification! There are just a few more questions that I
hope you may help me.

I used your script to calculate I² and found a high heterogeneity in my
model (86.63%).
#I²: http://www.metafor-project.org/doku.php/tips:i2_multilevel_multivariate
W <- diag(1/h_mc$vzf)
X <- model.matrix(model1)
P <- W - W %*% X %*% solve(t(X) %*% W %*% X) %*% t(X) %*% W
100 * sum(meta$sigma2) / (sum(meta$sigma2) + (meta$k-meta$p)/sum(diag(P)))

Do you have suggestions on how to handle with high heterogeneity among
effect sizes? How may I conduct sensitivity tests in a multilevel
meta-analysis using metafor? I identified (using a funnel plot) and removed
outliers to reduce the heterogeneity and redo the model. Then, I compared
the results of both models to evaluate if there is any discrepancies. Is
this approach suitable to evaluate potential bias in the results? Or are
there better alternatives?

Best wishes,

Rafael.
__________________________________________________________

Dr. Rafael Rios Moura
*scientia amabilis*

Behavioral Ecologist, PhD
Postdoctoral Researcher
Universidade Estadual de Campinas (UNICAMP)
Campinas, São Paulo, Brazil

Currículo Lattes: http://lattes.cnpq.br/4264357546465157
ORCID: http://orcid.org/0000-0002-7911-4734
Research Gate: https://www.researchgate.net/profile/Rafael_Rios_Moura2




<http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4244908A8>


Em qui, 8 de nov de 2018 às 13:48, Viechtbauer, Wolfgang (SP) <
wolfgang.viechtbauer using maastrichtuniversity.nl> escreveu:

> As for the model to use:
>
> In general, you want to use: ~1|studyID/effectsizeID
>
> Using list(~1|effectsizeID, ~1|studyID) may be correct if effectsizeID is
> unique for every row.
>
> This is essentially a question of 'explicit' versus 'implict' nesting. See
> also:
>
> https://stat.ethz.ch/pipermail/r-sig-meta-analysis/2018-July/000896.html
>
> Best,
> Wolfgang
>
> -----Original Message-----
> From: Rafael Rios [mailto:biorafaelrm using gmail.com]
> Sent: Sunday, 04 November, 2018 0:32
> To: Viechtbauer, Wolfgang (SP)
> Cc: Michael Dewey; r-sig-meta-analysis using r-project.org
> Subject: Re: [R-meta] Questions about Omnibus tests
>
> Dear Wolfgang,
>
> Could you please help me again with new questions?
>
> Should I build model1 rather than model2 to control for the dependency
> among studyID and effectsizeID?
>
> model1=rma.mv(zf, vzf, mods=~mate_choice,
> random=list(~1|studyID/effectsizeID, ~1|species1), data = h_mc)
> model2=rma.mv(zf, vzf, mods=~mate_choice, random=list(~1|effectsizeID,
> ~1|studyID, ~1|species1), data = h_mc)
>
> I used your script to calculate I² and found a high heterogeneity in my
> model (86.63%).
> #I²:
> http://www.metafor-project.org/doku.php/tips:i2_multilevel_multivariate
> W <- diag(1/h_mc$vzf)
> X <- model.matrix(model1)
> P <- W - W %*% X %*% solve(t(X) %*% W %*% X) %*% t(X) %*% W
> 100 * sum(meta$sigma2) / (sum(meta$sigma2) + (meta$k-meta$p)/sum(diag(P)))
>
> Do you have suggestions on how to handle with high heterogeneity among
> effect sizes? How may I conduct sensitivity tests in a multilevel
> meta-analysis using metafor? I identified (using a funnel plot) and removed
> outliers to reduce the heterogeneity and redo the model. Is this approach
> suitable to evaluate potential bias in results? Or are there better
> alternatives?
>
> Best wishes,
>
> Rafael.
> __________________________________________________________
>
> Dr. Rafael Rios Moura
> scientia amabilis
>
> Behavioral Ecologist, PhD
> Postdoctoral Researcher
> Universidade Estadual de Campinas (UNICAMP)
> Campinas, São Paulo, Brazil
>
> Currículo Lattes: http://lattes.cnpq.br/4264357546465157
> ORCID: http://orcid.org/0000-0002-7911-4734
> Research Gate: https://www.researchgate.net/profile/Rafael_Rios_Moura2
>

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