Message-ID: <5F43810A-3928-417D-AA53-4DE82C9AC9D5@gmail.com>
Date: 2019-10-02T13:00:20Z
From: Tina Dudenhöffer
Subject: [R-meta] Weight argument in rma.uni models
In-Reply-To: <49ac6b623102423f8cb808546c086ac9@UM-MAIL3214.unimaas.nl>
Dear Wolfgang,
thanks for your quick response. I, indeed, mean rma.mv()!
Considering the default is the inverse variance weight, would you suggest I stick to my res5 version?
> res5 <- rma.mv(EffectSize_NEW, Variance_New, method="REML",random = list(~ 1 | EffectSize_ID_NEW, ~ 1 | Study), data=Data)
> res5
I saw somewhere else the argument ?weighted=TRUE? added - but when looking the documentation, I don?t see it. I suppose it?s not necessary or at least not in my case?
Thank you so much!
Tina
> On Oct 2, 2019, at 2:49 PM, Viechtbauer, Wolfgang (SP) <wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:
>
> Dear Tina,
>
> I assume you mean the rma.mv() function, not rma.uni().
>
> If you don't specify W, then weights are applied automatically. See:
>
> https://wviechtb.github.io/metafor/reference/rma.mv.html
>
> and search for "Together with the variance-covariance matrix of the sampling errors". However, for the model you show, the model implied marginal variance-covariance matrix of the observed outcomes (M) is not diagonal, but also has off-diagonal elements. So, there is actually an entire weight matrix.
>
> Also, in 'res5', M (and hence the weight matrix W = M^(-1)) will incorporate the estimates of the two variance components (for EffectSize_ID_NEW and Study), while 'res6' only uses 1/Variance_New as the weights and doesn't consider the two variance components.
>
> Best,
> Wolfgang
>
> -----Original Message-----
> From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org] On Behalf Of Tina Dudenh?ffer
> Sent: Wednesday, 02 October, 2019 13:48
> To: r-sig-meta-analysis at r-project.org
> Subject: [R-meta] Weight argument in rma.uni models
>
> Dear all,
>
> I am working with the rma.uni function to fit a multivariate random effects model.
>
> I see that the W argument is an optional argument to specify a user-defined weight matrix. I was curious if any weight is applied if I don?t specify this argument.
> Specifically, I am wondering if the inverse variance weight is applied ?automatically?, considering I am specifying the V argument in the model itself.
>
> In terms of my model, I am wondering about the difference between these:
>
> res5 <- rma.mv(EffectSize_NEW, Variance_New, method="REML",random = list(~ 1 | EffectSize_ID_NEW, ~ 1 | Study), data=Data)
> res5
>
> res6 <- rma.mv(EffectSize_NEW, Variance_New, W=weight, method="REML",random = list(~ 1 | EffectSize_ID_NEW, ~ 1 | Study), data=Data)
> res6
>
> Note: the argument weight in my dataset is simply: 1/Variance_New
>
> Hope this is all clear.
>
> Many thanks and kind regards,
> Tina