Dear Fernanda,
Currently, there is no option in metafor that will automatically give you
standardized coefficients for meta-regression models. The question is also how
you would like to standardize those coefficients. In the usual regression
models, the standardized coefficients are those that you would obtain if both
the dependent and the independent variables are all rescalled to have a mean of
0 and a standard deviation of 1.
For meta-regression models, I don't see how rescalling the dependent variable
(i.e., the outcome) would give you something sensible. There are some
additional issues with the fact that you would also have to rescale the
sampling variances accordingly.
One possibility may be to just rescale the predictors. If this is what you
want, then you can always just rescale the variables manually (the scale()
function will help you do that).
For example:
data(dat.bcg)
dat <- escalc(measure="RR", ai=tpos, bi=tneg, ci=cpos, di=cneg, data=dat.bcg,
append=TRUE)
res <- rma(yi, vi, mods=cbind(ablat, year), data=dat, method="REML")
res
dat$ablat.std <- c(scale(dat$ablat))
dat$year.std <- c(scale(dat$year))
res <- rma(yi, vi, mods=cbind(ablat.std, year.std), data=dat, method="REML")
res
Part of the output:
estimate se zval pval ci.lb ci.ub
intrcpt -0.7321 0.1238 -5.9137 <.0001 -0.9748 -0.4895 ***
ablat.std -0.4046 0.1478 -2.7371 0.0062 -0.6943 -0.1149 **
year.std 0.0209 0.1605 0.1299 0.8966 -0.2938 0.3355
So, the results indicate that, for a one standard deviation increase in
absolute latitude, the relative risk decreases on average by .41 points. And
for a one standard deviation increase in year, the relative risk increases on
average by .02 points.
Whether one can determine the relative importance of predictors this way (this
at least seems to be the reason why people often ask for standardized
coefficients) is another issue.
Best,
--
Wolfgang Viechtbauer
Department of Psychiatry and Neuropsychology
School for Mental Health and Neuroscience
Maastricht University, P.O. Box 616
6200 MD Maastricht, The Netherlands
Tel: +31 (43) 368-5248
Fax: +31 (43) 368-8689
Web: http://www.wvbauer.com
----Original Message----
From: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org] On Behalf Of Fernanda Melo
Carneiro Sent: Wednesday, January 12, 2011 20:18 To:
r-h...@stat.math.ethz.ch Subject: [R] metafor/ meta-regression
> Hi I have tryed to do the meta-regression in metafor package, but I
> would like to get the standardized coefficients for each variable,
> however in command:
>
> res<-rma.uni (yi, vi, method="REML",
> mods=~cota+DL+uso+gadiente+idade, data=turbidez)
>
> I just have the coefficients no standardized (estimate) of the
> multiple regression.
>
> What I need to do?
>
> Thanks
>
> Fernanda Melo Carneiro contato: (62) 3521-1480 e 8121-7374
> www.ecoevol.ufg.br Laboratório de Ecologia Teórica e Síntese (UFG)
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