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--></style></head><body lang=EN-GB link=blue vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><div><p class=MsoNormal style='background:white'><span style='color:black'>Dear Michael</span></p><p class=MsoNormal style='background:white'><o:p> </o:p></p><p class=MsoNormal style='background:white'><span style='color:black'>Apologies, I thought i had started a new thread.</span></p><p class=MsoNormal style='background:white'><o:p> </o:p></p><p class=MsoNormal style='background:white'><span style='color:black'>I have checked the SDs and omitted any that are zero, so I don’t think that is the problem. I am more worried by the warning “</span><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>Studies with non-positive standard deviation get no weight in meta-analysis” I assume this signifies that means with a standard deviations of greater value than the mean are ignored (eg mean</span><span style='color:black'> ±</span><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'> SD = 10</span><span style='color:black'> ±</span><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'> 14). Is that correct?<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>Thanks<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>Mark</span></p><p class=MsoNormal style='background:white'><span style='color:black'><br></span><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A;background:white'>On Friday, 10 March 2023 at 14:24:55 CET, Michael Dewey <lists@dewey.myzen.co.uk> wrote:</span></p><p class=MsoNormal style='background:white'><o:p> </o:p></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>Dear Mark<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>First of all please do not hijack an old thread but start a new one as<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>your e-mail (and my reply) appear to be about marginal means in the archive.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>Have you checked the standard deviations? I assume some are zero which<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>explains both your messages. It is likely the package then drops them.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>Michael<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>On 10/03/2023 11:46, mark walton via R-sig-meta-analysis wrote:<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> Dear All<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> I wonder if some one can help.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> 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))<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> 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.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> But the model converges and I get means and confidence intervals, and significant differences between subgroups<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> 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.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> ddply(MP_global, .(Ecosystem), function(x) data.frame(wret=weighted.mean(x$meanMP_per_m2, x$Sample_no)))<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> Can anyone shed some light? Is it because metamean is ignoring some values?<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>> Thanks very muchMark<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#1D2228'>><o:p> </o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Sent from <a href="https://go.microsoft.com/fwlink/?LinkId=550986">Mail</a> for Windows</p><p class=MsoNormal><o:p> </o:p></p></div></body></html>