Message-ID: <25402659-688c-ee0e-8b94-c7d5f23b9d83@dewey.myzen.co.uk>
Date: 2023-03-10T13:24:50Z
From: Michael Dewey
Subject: [R-meta] Metamean
In-Reply-To: <2077535677.1197651.1678448809558@mail.yahoo.com>
Dear Mark
First of all please do not hijack an old thread but start a new one as
your e-mail (and my reply) appear to be about marginal means in the archive.
Have you checked the standard deviations? I assume some are zero which
explains both your messages. It is likely the package then drops them.
Michael
On 10/03/2023 11:46, mark walton via R-sig-meta-analysis wrote:
> Dear All
> I wonder if some one can help.
> I am using metamean to determine with of my habitats have the most microplastics, I have collected 400+ papers with means, SD and sample number.Using the command:-metamean(MP_global, mean=meanMP_per_m2, na.rm=TRUE, sd=MP_SD, na.rm=TRUE,n=Sample_no, na.rm=TRUE ,byvar=Ecosystem, na.rm=TRUE,comb.random=TRUE,comb.fixed=FALSE,verbose=TRUE, control=list(maxiter=1000))
>
> I get some repeated warnings:?Warning: Studies with non-positive standard deviation get no weight in meta-analysis.Warning: Ratio of largest to smallest sampling variance extremely large. May not be able to obtain stable results.
>
> But the model converges and I get means and confidence intervals, and significant differences between subgroups
> However when I estimate my own mean values for each habitat weighted by sample number (below) the values are very different for some, and I am worried that the metamean results are not a true reflection of the data.
> ddply(MP_global, .(Ecosystem),? function(x) data.frame(wret=weighted.mean(x$meanMP_per_m2, x$Sample_no)))
>
> Can anyone shed some light? Is it because metamean is ignoring some values?
> Thanks very muchMark
>
> [[alternative HTML version deleted]]
>
> _______________________________________________
> R-sig-meta-analysis mailing list @ R-sig-meta-analysis at r-project.org
> To manage your subscription to this mailing list, go to:
> https://stat.ethz.ch/mailman/listinfo/r-sig-meta-analysis
>
--
Michael
http://www.dewey.myzen.co.uk/home.html