[R-meta] Zero event

[Viechtbauer, Wolfgang (NP)]

With a rare outcome like that, the usual method of handling 0 cells (adding 1/2's) is indeed not ideal. Alternatively, one could use methods based on exact likelihoods, such as logistic regression type models. For example, using the data below:

library(metafor)

dat <- read.table(header=TRUE, text = "
        ai      bi      ci      di
Study1  1       19      0       20
Study2  1       28      0       29
Study3  0       26      7       25
Study4  0       42      0       42")

res <- rma(measure="RR", ai=ai, bi=bi, ci=ci, di=di, data=dat, method="EE")
res
predict(res, transf=exp)

res <- rma.glmm(measure="RR", ai=ai, bi=bi, ci=ci, di=di, data=dat, method="EE")
res
predict(res, transf=exp)

The two approaches yield rather different results.

Notes:

1) I used an equal-effects model, because with 4 studies, trying to fit a random-effects model seems a bit 'ambitious'.

2) In the rma.glmm() approach, studies with 0 events in both arms are automatically dropped. This is because the likelihood is flat, at least when the outcome measure is the (log) odds ratio.

3) Using (log) risk ratios as the outcome measure with rma.glmm() is an experimental feature that I added recently. It seems to work ok here, but might fail in other cases.

One can also use methods like the Mantel-Haenszel and Peto's method here:

rma.mh(measure="RR", ai=ai, bi=bi, ci=ci, di=di, data=dat)
rma.peto(measure="RR", ai=ai, bi=bi, ci=ci, di=di, data=dat)

These yield quite similar results as the logistic regression approach.

But in the end, trying to squeeze something out of such little data is difficult, which is also reflected in the wide CIs.

Best,
Wolfgang

>-----Original Message-----
>From: Klaow sota [mailto:jija_99 using hotmail.com]
>Sent: Monday, 19 September, 2022 13:09
>To: Viechtbauer, Wolfgang (NP); r-sig-meta-analysis using r-project.org
>Subject: Re: Zero event
>
>Thank you so much.
>
>The example:  some case(s) are zero after treatment, then when we run for RR and
>effect size, it probably showed the incorrect result.
>
>Best,
>Klaow
>
>        Treatment       Control
>        TB+     TB-     TB+     TB-
>Study1  1       19      0       20
>Study2  1       28      0       29
>Study3  0       26      7       25
>Study4  0       42      0       42
>
>________________________________________
>From: Viechtbauer, Wolfgang (NP) <wolfgang.viechtbauer using maastrichtuniversity.nl>
>Sent: Monday, September 19, 2022 6:01 PM
>To: r-sig-meta-analysis using r-project.org <r-sig-meta-analysis using r-project.org>
>Cc: Klaow sota <jija_99 using hotmail.com>
>Subject: RE: Zero event
>
>I am not sure I quite understand. Can you provide a reproducible example to
>illustrate the issue? In what sense is the result incorrect?
>
>Best,
>Wolfgang
>
>>-----Original Message-----
>>From: Klaow sota [mailto:jija_99 using hotmail.com]
>>Sent: Monday, 19 September, 2022 12:57
>>To: Viechtbauer, Wolfgang (NP); r-sig-meta-analysis using r-project.org
>>Subject: Re: Zero event
>>
>>I run from the positive/negative cases to find Risk ratio. When I run the zero
>>event, it affects the RR and make it incorrect result.
>>Is any code that can manipulate the zero event?
>>
>>Thank you very much.
>>
>>Best,
>>Klaow
>>
>>________________________________________
>>From: Viechtbauer, Wolfgang (NP) <wolfgang.viechtbauer using maastrichtuniversity.nl>
>>Sent: Monday, September 19, 2022 4:31 PM
>>To: r-sig-meta-analysis using r-project.org <r-sig-meta-analysis using r-project.org>
>>Cc: Klaow sota <jija_99 using hotmail.com>
>>Subject: RE: Zero event
>>
>>Dear Klaow,
>>
>>What kind of effect size / outcome measure are you using?
>>
>>Best,
>>Wolfgang
>>
>>>-----Original Message-----
>>>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On
>>>Behalf Of Klaow sota
>>>Sent: Monday, 19 September, 2022 11:29
>>>To: r-sig-meta-analysis using r-project.org
>>>Subject: [R-meta] Zero event
>>>
>>>Dear everyone,
>>>
>>>If my data appear zero event, Is any function/code that can improve this
>>>phenomenon without cutting the study?
>>>I would like to get the effect size and sd/variance. Thank you.
>>>
>>>Best,
>>>Klaow