[R-meta] Antwort: RE: metafor - averaging over rma result

steph@@ie@wi@keibei@er m@iii@g oii bii@uzh@ch steph@@ie@wi@keibei@er m@iii@g oii bii@uzh@ch
Thu Oct 24 20:17:51 CEST 2019

Dear Wolfgang, 

thanks a lot for your swift and helpful reply!

Do I understand correctly that you, from a statistical point of view, would not 
recommend aggregating over the rma results by disorder and then plotting those in a
forest plot, considering that this would not accurately represent the overall intercept
as well as would lead to a bias in the VRs and corresponding CIs in the plot?

Thanks for your take on that.


-----"Viechtbauer, Wolfgang (SP)" <wolfgang.viechtbauer using maastrichtuniversity.nl> schrieb: -----
An: "stephanie.winkelbeiner using bli.uzh.ch" <stephanie.winkelbeiner using bli.uzh.ch>, "r-sig-meta-analysis using r-project.org" <r-sig-meta-analysis using r-project.org>
Von: "Viechtbauer, Wolfgang (SP)" <wolfgang.viechtbauer using maastrichtuniversity.nl>
Datum: 22.10.2019 17:03
Betreff: RE: [R-meta] metafor - averaging over rma result

Dear Stephanie,

My suggestion would be to fit a sensible model that uses 'disorder' as a predictor and then plot the model coefficients using the forest() function. Here is an example, not using VRs, but the idea is the same:


dat <- dat.bourassa1996

# calculate log(OR) and corresponding sampling variances
dat <- escalc(measure="OR", ai=lh.le, bi=lh.re, ci=rh.le, di=rh.re, data=dat)

# fit model
res <- rma(yi, vi, mods = ~ eye_assess - 1, data=dat, subset=sex=="combined")

# by removing the intercept, the coefficients are the estimated log(OR)s for each level of 'eye_assess'

# pass coefficients and variance of the coefficients to forest() function
forest(coef(res), diag(vcov(res)), slab=names(coef(res)), atrans=exp, 
       at = c(log(c(1, 2, 4, 8, 16, 32))), xlab="Odds Ratio (log scale)")


-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On Behalf Of stephanie.winkelbeiner using bli.uzh.ch
Sent: Tuesday, 22 October, 2019 15:44
To: r-sig-meta-analysis using r-project.org
Subject: [R-meta] metafor - averaging over rma result

Dear experts, 

for a meta-analysis, we calculated the variability ratio (VR) of all included studies
using the rma function of the metafor package.

We would like to plot the results in a forest plot grouped by disorder for a less 
busy presentation (compared to plotting the VR for every study).

Yet, averaging over the VRs, especially over the confidence intervals seems

Do you have any suggestions?

Thank you, 

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