Dear Mario,
If you could tell me how to define and interpret I^2 and H^2 for models with
moderators, I may consider implementing these measures for such models. However,
I am not aware of any work that has extended these measures to meta-regression
models.
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-bounces at r-project.org [mailto:r-help-bounces at
r-project.org]
> On Behalf Of petretta at unina.it
> Sent: Sunday, February 20, 2011 13:59
> To: r-help at r-project.org
> Subject: [R] Help Metafor
>
> Dear Sir, I'm using the "Metafor" package;
>
> however, introducing moderators, I'm unable to obtain both I^2 (%
> of total variability due to heterogeneity) and H^2 (total variability
> / within-study variance). It is possible to obtain I^2 and H^2 also
> with moderators?
>
> As example
>
> _Dataset <- sqlQuery(channel = 1, select * from [Foglio1$])
> names(Dataset) <- make.names(names(Dataset))
> alloc.a <- ifelse(dat$alloc == "a", 1, 0)
> alloc.b <- ifelse(dat$alloc == "b", 1, 0)
> alloc.c <- ifelse(dat$alloc == "c", 1, 0)
>
> res<-rma.uni(yi, vi, mods=cbind(alloc.a, alloc.b, Year),
> measure="GEN", intercept=TRUE, data=dat, slab=Author, subset,
add=1/2,
> to="only0", vtype="LS", method="REML",
weighted=TRUE, knha=FALSE,
> btt=c(2,3))
>
> >?print (res)
>
> Mixed-Effects Model (k = 22; tau^2 estimator: REML)
> tau^2 (estimate of residual amount of heterogeneity): 0.7810 (SE =
0.2924)
> tau (sqrt of the estimate of residual heterogeneity): 0.8838
>
> Test for Residual Heterogeneity:
> QE(df = 18) = 223.3159, p-val < .0001
>
> Test of Moderators (coefficient(s) 2,3):
> QM(df = 2) = 0.8251, p-val = 0.6620
>
> Model Results:
>
> ????????? estimate?????? se???? zval??? pval????? ci.lb???? ci.ub
> intrcpt? -135.3524? 54.4487? -2.4859? 0.0129? -242.0700? -28.6349? *
> alloc.a??? -0.3836?? 0.4529? -0.8469? 0.3971??? -1.2713??? 0.5042
> alloc.b??? -0.3656?? 0.5529? -0.6613? 0.5084??? -1.4493??? 0.7180
> Year??????? 0.0673?? 0.0273?? 2.4677? 0.0136???? 0.0139??? 0.1208? *
>
> Many thanks
>
> _________________________________________
>
> Mario Petretta
> Dipartimento di Medicina Clinica Scienze Cardiovascolari e Immunologiche
> Facolt? di Medicina e Chirurgia
> Universit? di Napoli Federico II
> 081 - 7462233