[R-meta] specification of phi in vcalc

[Lukasz Stasielowicz]

Dear Danielle,

vcalc documentation contains a potentially helpful tip: "Argument phi 
must then also be specified to indicate the autocorrelation among the 
sampling errors of two effect sizes that differ by one unit on the time1 
variable. As above, the autocorrelation of the measurements themselves 
can be used here as a proxy."
https://rdrr.io/github/wviechtb/metafor/man/vcalc.html

Perhaps some tables in primary studies show correlations between 
neighboring time points?

Another option: If raw data are available for some primary studies, then 
one could estimate the correlation for several data sets and use it as 
"phi" input for vcalc. If different data sets lead to different values, 
then one could test different values in sensitivity analyses.




Best,
Lukasz
-- 
Lukasz Stasielowicz
Osnabrück University
Institute for Psychology
Research methods, psychological assessment, and evaluation
Seminarstraße 20
49074 Osnabrück (Germany)

See also:
On 03.08.2022 12:00, r-sig-meta-analysis-request using r-project.org wrote:
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>     1. specification of phi in vcalc (Danielle Hiam)
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> Message: 1
> Date: Wed, 3 Aug 2022 06:54:48 +0000
> From: Danielle Hiam <danielle.hiam using deakin.edu.au>
> To: "r-sig-meta-analysis using r-project.org"
> 	<r-sig-meta-analysis using r-project.org>
> Subject: [R-meta] specification of phi in vcalc
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> Hello,
> 
> I am running a meta-analysis that has nested data and dependent effect sizes (multiple timepoints). Therefore, I need to take into account effect sizes that are correlated and also cluster within studies. I will run vcalc, then the rma.mv function and then use robust with clubsandwich set to true to "correct" for any mis-specification of the model. However, I am looking for some clarification regarding how to "guess" the value for phi in the vcalc function, R code: V <- vcalc(FC_SD, cluster, time1=Time_NUM, data, phi=0.6).
> 
> When I change phi from 0.6 to 0.8 in vcalc I get very different results from the meta-analysis (rma.mv followed by robust(.... Clubsanwich=T). I have read James Pustejovsky paper (DOI: https://doi.org/10.1007/s11121-021-01246-3) on this, where he suggests that in situations where no information is available, the meta-analyst might pick a plausible value and then conduct sensitivity analysis across a range reasonable values. How would I go about this?
> 
> Any information regarding specification of phi would be greatly appreciated
> 
> Thanks,
> Danielle
> 
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