[R-meta] Obtaining study-level effect size and sampling variance through robust variance models

Mon, Mar 11, 2019 2:00 AM

Dear Mutlu,

I just simulated some data to illustrate the plotting. There was no particular reason I used a uniform for simulating the sampling variances. As for the outcomes, the standard models assume that the sampling distributions are normal, so that is why I simulated 'yi' from a normal distribution.

Best,
Wolfgang

-----Original Message-----
From: Mutlu Umaroglu [mailto:mutlu.umaroglu at hacettepe.edu.tr] 
Sent: Monday, 11 March, 2019 8:28
To: Viechtbauer, Wolfgang (SP); r-sig-meta-analysis at r-project.org
Subject: Re: [R-meta] Obtaining study-level effect size and sampling variance through robust variance models

Dear Viechtbauer and all,

In this scenarios, vi follows uniform distribution and yi follows normal 
distribution. vi~U(.01,1) and yi~N(0,vi+.5=T^2).

Why vi follows uniform distribution? Is uniform distribution more robust 
than others?

Other words, what is the recommended distribution (and value) of Yi and 
Vi in a typical simulation scenario for meta analysis? And Why?

10-03-2019 14:01, Viechtbauer, Wolfgang (SP) yazm??:

Plus addpoly(), to add a summary polygon to the forest plot that shows
the results from robu(). For example:

library(metafor)
library(robumeta)

set.seed(1002)
dat <- data.frame(vi = runif(20, .01, 1))
dat$yi <- rnorm(20, 0, sqrt(dat$vi + .5))
dat$study <- sort(sample(1:10, 20, replace=TRUE))

res <- robu(yi ~ 1, var.eff.size = vi, studynum = study, data=dat)
res

forest(dat$yi, dat$vi, ylim=c(-1.5,res$M+3), slab=paste("Study",
dat$study), cex=1)
abline(h=0)
addpoly(res$reg_table$b.r, ci.lb=res$reg_table$CI.L,
ci.ub=res$reg_table$CI.U, cex=1)

Best,
Wolfgang

-----Original Message-----
From: R-sig-meta-analysis
[mailto:r-sig-meta-analysis-bounces at r-project.org] On Behalf Of
Michael Dewey
Sent: Saturday, 02 March, 2019 14:18
To: Mufan Luo; r-sig-meta-analysis at r-project.org
Subject: Re: [R-meta] Obtaining study-level effect size and sampling
variance through robust variance models

Dear Mufan

You do not need to fit a model with rma.uni to use forest.

library(metafor)
?forest.default

Michael

On 01/03/2019 18:16, Mufan Luo wrote:

Dear meta-analysists,
Hope this email finds you well.
I am conducting a meta-analysis using robust variance model. To create 
forest plot for each study, I?d like to obtain mean effect size and 
sampling variance for each study.
I decided to use forest function in metafor to create the forest 
plots.
Since the forest function only accepts rma file, I am trying to fit a 
rma model (rather than rma.uni) that produces the same coefficient, 
95% CI and p-value as the robu model.
For example, below is my robu model,
run.anxiety <- robu(formula = Fisher.s.Z ~ 1,
                     var.eff.size = Fisher_var,
                     data = anxiety,
                     studynum = Study,
                     modelweights = "CORR")
According to prior discussion about converting robu to rma.uni in this 
mail list, I also calculated the number of studies k in cluster j, 
average of sampling variance Vbar, and tau square.

tau_sq_robu_anx <- as.numeric(run.anxiety$mod_info$tau.sq)
anxiety$k <- with(anxiety, table(Study)[Study])
anxiety$Vbar <- with(anxiety, tapply(Fisher_var, Study, mean)[Study])

I am trying to get the weight and plug it into the following model,

rma(yi = weightedES, vi = ??, data = weighted)

However, I am not sure if the correct calculation is

anxiety$Vnew <- with(anxiety, as.numeric(Vbar + tau_sq_robu_anx)

Thank you so much for our attention.
Best,
Mufan

[R-meta] Obtaining study-level effect size and sampling variance through robust variance models

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