[R-meta] Difference in Proportions Meta-Analysis

Mon, Jun 8, 2020 8:27 AM

I am not sure I really understand what you did. arm1_prop_plogis and arm2_prop_plogis actually sound like they are plogis()-transformed proportions, which doesn't make sense (plogis() is the inverse-logit transformation). The logit transformation is qlogis(). Not sure how you computed arm1_se and arm2_se. Why not use escalc(measure="PLO", ...), which will do things correctly for you?

But if you want to compare the two groups within studies directly, then you need to use measures such as the risk difference (measure="RD"), the log transformed risk ratio ("RR"), or the log transformed odds ratio ("OR"). In fact, the difference between two logit-transformed proportions *IS* the log transformed odds ratio.

So, just use escalc(measure="OR", ...) and then pass the 2x2 table counts via arguments 'ai', 'bi', 'ci', 'di' (or the 'event' counts via arguments 'ai' and 'ci' and the group sizes via 'n1i' and 'n2i'). See help(escalc) and search for "OR".

Best,
Wolfgang

-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org]
On Behalf Of ne gic
Sent: Monday, 08 June, 2020 15:09
To: Michael Dewey
Cc: r-sig-meta-analysis at r-project.org
Subject: Re: [R-meta] Difference in Proportions Meta-Analysis

Dear Michael,

Thanks. I am using metafor (or rather planning to for this).

Initially I had performed two separate single arm meta-analysis of
proportion as follows to get an estimate for each of the arms:

rma(yi = arm1_prop_plogis, sei = arm1_se, slab=author_year ,
data=gastric_data, method="REML")

rma(yi = arm2_prop_plogis, sei = arm2_se, slab=author_year ,
data=gastric_data, method="REML")

But then it was pointed out that it would be more interesting to
meta-analyze the difference in proportions from both arms, and hence my
question.

So what I have done is:

  1. Calculate the raw proportion differences i.e. before using the R
  function "qlogis"
  2. Calculate a single SE from the SE of both arms using the equation
  provided by Wolfgang.

Then the two outputs are what I hope to provide as inputs to rma exactly as
I had done before for the single arm analysis.

Is there a more direct way to do this? or am I missing something?

Thanks for your help,

Sincerely,
nelly

On Mon, Jun 8, 2020 at 2:48 PM Michael Dewey <lists at dewey.myzen.co.uk>
wrote:

Dear Nelly

I am not sure what software you use but both meta and metafor provide
analysis of risk differences (which is what differences in proportions
are) so you may get what you want directly there.

Michael

On 08/06/2020 11:36, ne gic wrote:

Dear List,

I aim to perform a meta-analysis and present a forest plot of the
difference in proportions between two groups.

For each group I have proportion and standard error (SE).

It's straightforward to get the difference in the proportions, but am

not

sure how to handle the SEs, I presume I can't just subtract them. Is

there

a formula on how to handle SEs?

Sincerely,
nelly

[R-meta] Difference in Proportions Meta-Analysis

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