[R-meta] Cannot fit model: rma.glmm with zero events

[Jonathan C. Lau]

Hi Wolfgang,

Thanks for the very clear explanation.

I've integrated your suggestions into my script. For forest plot
visualization, everything remains the same except for the addpoly() call to
the zero event subgroup:

pt <- prop.test(0, 304)
addpoly(x=pt$estimate, ci.lb=pt$conf.int[1], ci.ub=pt$conf.int[2],
cex=0.75, mlab="FE Model for Subgroup (Zero Events)", digits=3)

rather than my typical RE Model addpoly line:
addpoly(res_IG_Y_modern_N, cex=0.75, transf=transf.ilogit, mlab="RE Model
for Subgroup", digits=3)

-jon

On Sat, Mar 3, 2018 at 5:46 AM Viechtbauer Wolfgang (SP) <
wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:

> Hi Jon,
>
> The error stems from lme4, which refuses (appropriately!) to fit this
> model when there are zero events.
>
> Fitting the FE model does work:
>
> res_IG_Y_frameless <- rma.glmm(measure="PLO", xi=num, ni=denom, data=df,
> slab=UniqueID, subset=(igns=="Y" & frame_type=='frameless'), method="FE")
>
> But the log odds is technically -Inf here. That's pretty much what the
> estimate of -28.1801 indicates.
>
> Since you have no way of estimating heterogeneity here, you could assume
> homogeneity, in which case you are in a situation where you have a binomial
> distribution with:
>
> sum(df[df$igns=="Y" & df$frame_type=='frameless',"denom"])
>
> trials (i.e., 304) with 0 observed events (the sum of independent
> binomials with the same true probability is the same as a binomial with the
> the total number of trials). Then a CI (computed by inverting the score
> test) for the true proportion can be obtained with:
>
> prop.test(0, 304)
>
> Or, using the rule of three (
> https://en.wikipedia.org/wiki/Rule_of_three_(statistics)):
>
> 3/304
>
> is the upper bound (the lower bound is obviously 0).
>
> Best,
> Wolfgang
>
> >-----Original Message-----
> >From: jonathan.c.lau at gmail.com [mailto:jonathan.c.lau at gmail.com] On
> >Behalf Of Jonathan C. Lau
> >Sent: Friday, 02 March, 2018 21:20
> >To: r-sig-meta-analysis at r-project.org
> >Cc: Viechtbauer Wolfgang (SP)
> >Subject: Cannot fit model: rma.glmm with zero events
> >
> >ATTACHMENT(S) REMOVED: test.csv | glmm_problem.R
> >
> >Hi there,
> >
> >I am performing a meta-analysis of proportions where the event rates are
> >logit-transformed (PLO) prior to random effects modeling. In the main
> >analysis, where events are not as sparse, I have been able to run
> >rma.glmm without any problems. However, when performing the subgroup
> >analysis, I have some situations where there are zero events in one of
> >the groups, resulting in the following error: "Error in rma.glmm(measure
> >= "PLO", xi = num, ni = denom, data = df, slab = UniqueID,  :  Cannot fit
> >ML model." See below for the log. I've also attached a basic example with
> >.csv and .R code.
> >
> >Can you please advise?
> >
> >Happy to provide more details if necessary.
> >
> >Thanks,
> >jon
> >
> >--
> >
> >> rm(list=ls())
> >>
> >> # meta-analysis code example for metafor
> >> library(metafor)
> >> library(lme4)
> >>
> >> # citing metafor package
> >> citation(package='metafor')
> >
> >To cite the metafor package in publications, please use:
> >
> >  Viechtbauer, W. (2010). Conducting meta-analyses in R with the
> >  metafor package. Journal of Statistical Software, 36(3), 1-48.
> >  URL: http://www.jstatsoft.org/v36/i03/
> >
> >A BibTeX entry for LaTeX users is
> >
> >  @Article{,
> >    title = {Conducting meta-analyses in {R} with the {metafor} package},
> >    author = {Wolfgang Viechtbauer},
> >    journal = {Journal of Statistical Software},
> >    year = {2010},
> >    volume = {36},
> >    number = {3},
> >    pages = {1--48},
> >    url = {http://www.jstatsoft.org/v36/i03/},
> >  }
> >
> >> packageVersion('metafor') # to know current version number
> >[1] ‘1.9.9’
> >>
> >> df <- read.table('test.csv', header = TRUE, sep = ',')
> >> res_IG_Y <- rma.glmm(measure="PLO", xi=num, ni=denom, data=df,
> >slab=UniqueID)
> >>
> >> ### fit random-effects model in the two subgroups
> >> res_IG_Y_frameless <- rma.glmm(measure="PLO", xi=num, ni=denom,
> >data=df, slab=UniqueID, subset=(igns=="Y" & frame_type=='frameless')) #
> >zero
> >Error in rma.glmm(measure = "PLO", xi = num, ni = denom, data = df, slab
> >= UniqueID,  :
> >  Cannot fit ML model.
> >> res_IG_Y_frame <- rma.glmm(measure="PLO", xi=num, ni=denom, data=df,
> >slab=UniqueID, subset=(igns=="Y" & frame_type=="frame"))
>

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