[R-meta] Question on combining means with robumeta

Wed, Aug 18, 2021 4:59 AM

Dear Tobias,

I don't understand what you mean by "Since in some cases I had negative values". Negative values where?

This aside, 'var.eff.size' is for the *variances* but SEM is the SE of the means. So it should be:

res <- robu(formula = Mean ~ 1, data = dat,
              studynum = Author, var.eff.size =SEM^2,
              rho = .8, small = TRUE, modelweights="CORR")
res

although the results are basically the same.

Second, LogMean_SEM doesn't seem to be computed correctly in your example and let's not call it SEM since it's a variance:

dat$LogMean_Var <- with(dat, SD^2/(N*Mean^2))

Now:

res1 <- robu(formula = LogMean ~ 1, data = dat,
             studynum = Author, var.eff.size =  LogMean_Var,
             rho = .8, small = TRUE, modelweights="CORR")
res1

#backtransformed results from log scale
round(exp(c(res1$reg_table$b.r[[1]],res1$reg_table$CI.L[[1]],res1$reg_table$CI.U[[1]])),2) 

gives very similar results as 'res' earlier.

Best,
Wolfgang

-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org] On
Behalf Of Tobias Saueressig
Sent: Tuesday, 17 August, 2021 17:48
To: Meta list
Subject: [R-meta] Question on combining means with robumeta

Dear All,

I have a question concerning the combination/pooling of means. Since most of my
studies are correlated I deceided to use robust variance estimation method to do
this. So metamean function in meta was out because of this. So I used robumeta.
Since in some cases I had negative values I deceided to use log transformed means
for pooling. My problem is that the estimates look reasonable now with robumeta
but the heterogeneity parameters(e.g. Tau, I?) are all estimated with zero. This
is strange. Does anybody know why that is?

Regards,
Tobias Saueressig

Reproducible example:

#Example
?Author <-c("Carboch et al. (2019)","Stare et al. (2015)","Mackie (2013)","Hornery
et al. (2007)",
"Takahashi et al. ( 2006)","Morante et al. (2005)","O'Donoghue, P. and Ingram, B.
(2001)",
"O'Donoghue, P. and Ingram, B. (2001)")

?Mean<-c(5.93,4.40,6.42,6.70,5.10,6.40,5.70,4.90)
?SD<-c(0.67,1.73,1.27,2.20,5.19,1.40,1.00,1.40)
?N<-c(7,5,9,17,16,12,24,35)
?SEM<-c(0.25,0.77,0.42,0.53,1.30,0.40,0.20,0.24)
?LogMean<-c(1.78,1.48,1.86,1.90,1.63,1.86,1.74,1.59)
?LogMean_SEM<-c(1.50,3.40,2.72,3.57,6.62,2.59,1.16,1.16)

?dat<-data.frame(Author,Mean,SD,N,SEM,LogMean,LogMean_SEM)

?#Formulas used
?#SEM<-SD/sqrt(N)
?#LogMean<-log(Mean)
?#LogMean_SEM<-SD^2/(N*Mean^2) => taken from metamean function in meta

?#normalscale
?res <- robu(formula = Mean ~ 1, data = dat,
? ? ? ? ? ? ? studynum = Author, var.eff.size =SEM,
? ? ? ? ? ? ? rho = .8, small = TRUE, modelweights="CORR")
?res

?#logscale
?res1 <- robu(formula = LogMean ~ 1, data = dat,
? ? ? ? ? ? ?studynum = Author, var.eff.size = ?LogMean_SEM,
? ? ? ? ? ? ?rho = .8, small = TRUE, modelweights="CORR")
?res1

?#backtransformed results from log scale
?round(exp(c(res1$reg_table$b.r[[1]],res1$reg_table$CI.L[[1]],res1$reg_table$CI.U[
[1]])),2)

[R-meta] Question on combining means with robumeta

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