[R-meta] Meta-analysis with proportion and mean data

[M West]

Thanks so very much - this is incredibly helpful!

On Wed, Aug 30, 2017 at 8:22 AM, Wolfgang Viechtbauer <
wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:

> Please keep the mailing list in cc.
>
> What you describe is a 'phylogenetic meta-analysis'. See, for example:
>
> Adams, D. C. (2008). Phylogenetic meta-analysis. Evolution, 62(3), 567-572.
>
> Lajeunesse, M. J. (2009). Meta-analysis and the comparative phylogenetic
> method. The American Naturalist, 174(3), 369-381.
>
> Nakagawa, S., & Santos, E. S. A. (2012). Methodological issues and
> advances in biological meta-analysis. Evolutionary Ecology, 26(5),
> 1253-1274.
>
> And yes, that can be done with the rma.mv() function. And yes, you would
> need to have a phylogeny for the species that you are dealing with, which
> in turn can be turned into a covariance/correlation matrix under certain
> assumptions (e.g., a Brownian motion model for trait evolution).
>
> Reading help(rma.mv) is a start. I do not currently have a nice dataset
> to illustrate this, but you can find an example (a rather complicated one
> with two phylogenies) described here:
>
> http://www.metafor-project.org/doku.php/tips:speeding_up_mod
> el_fitting#complex_models
>
> You can simplify this to a single phylogeny.
>
> The 'ape' package allows you to work with phylogenies (and can convert
> them to correlation matrices).
>
> Best,
> Wolfgang
>
> --
> Wolfgang Viechtbauer, Ph.D., Statistician | Department of Psychiatry and
> Neuropsychology | Maastricht University | P.O. Box 616 (VIJV1) | 6200 MD
> Maastricht, The Netherlands | +31 (43) 388-4170 | http://www.wvbauer.com
>
> On 08/29/2017 07:51 PM, M West wrote:
> Hi Wolfgang,
>
> Sorry, I think I wrote a very dumb question earlier - information overload
> and I tried to overly complicate the data. So I figured that question out.
> However, I do have another, hopefully, more sensible question: I read
> recently (citation below) that a unique problem for biological
> meta-analysis is that they often compare across many different species, and
> therefore, should correct for or at least account for the potential that
> phylogenetic relatedness could drive the observed pattern of interest in
> their particular analyses. I understand that these corrections are
> available in metafor - but I'm not having luck on finding any more detailed
> information on this topic. I.e., does this mean that in actuality,
> biological meta-analyses need to also know detailed (or just rough)
> phylogenetic relationships between the different species in their study
> (i.e., if the meta-analysis contains data with three different species of
> Drosophila, and monkeys, and sheep, how does one go about 'correcting for
> this'?). This particular recommendation seems valid, but a bit overwhelming
> considering that I do not work with phylogenies! Do I need to collaborate
> with someone who does so they can provide relatedness values for the data
> in the meta-analysis?
>
> Many thanks for your help!
>
> Meta-evaluation of meta-analysis: ten appraisal questions for biologists
> 2017 Nakawaga et al.
>
> On Tue, Aug 29, 2017 at 9:14 AM, Viechtbauer Wolfgang (SP) <
> wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:
> Dear M,
>
> I am not sure I fully understand. My interpretation of what you describe
> is this. The first group reports:
>
> 100 * (mean_post_treatment - mean_pre_treatment) / mean_pre_treatment
> 100 * (mean_post_control - mean_pre_control) / mean_pre_control
>
> or
>
> 100 * (mean_post_treatment - mean_pre_treatment) / mean_pre_treatment -
> 100 * (mean_post_control - mean_pre_control) / mean_pre_control
>
> while the second group reports:
>
> mean_post_treatment
> mean_post_control
>
> or
>
> mean_post_treatment - mean_post_control
>
> Is that correct? If not, please write our in some form what exactly is
> reported.
>
> Best,
> Wolfgang
>
> --
> Wolfgang Viechtbauer, Ph.D., Statistician | Department of Psychiatry and
> Neuropsychology | Maastricht University | P.O. Box 616 (VIJV1) | 6200 MD
> Maastricht, The Netherlands | +31 (43) 388-4170 | http://www.wvbauer.com
>
> -----Original Message-----
> From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bo
> unces at r-project.org] On Behalf Of M West
> Sent: Monday, August 28, 2017 23:09
> To: r-sig-meta-analysis at r-project.org
> Subject: [R-meta] Meta-analysis with proportion and mean data
>
> Hello,
>
> I am gathering data for a meta-analysis. So far, most of the studies report
> the results as the percentage reduction in the focal trait (i.e., percent
> weight loss) in the control group vs. the percentage reduction in the focal
> trait (percent weight loss) in the treatment group (and the SE). However, a
> small subset of studies report the actual means of the control (i.e., mean
> weight +/- SE) and the treatment (mean weight +/- SE).
>
> My question is, should I convert the smaller subset into proportions so
> that all of the data are the same (or v.v.,)? i.e., is that ok to do (i.e.,
> since I am using other people's data)? Or would it be better to analyze the
> data separately? (my apologies, I know this seems like a rather silly
> question, but I feel a bit stumped).
>
> Many thanks in advance for your helpful (and patient) answers!
>
> Best,
> ~M
>

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