[R-meta] questions on some functions in metafor and clubsandwich
Brendan Hutchinson
Brend@n@Hutch|n@on @end|ng |rom @nu@edu@@u
Wed Feb 9 07:54:29 CET 2022
Hi mailing list,
Thanks in advance for any help regarding my questions - I have two and they concern the metafor and clubsandwich packages, and multilevel modelling.
1. My first question concerns the difference between the robust() function in metafor and the coef_test() function in clubsandwich - I'm a little confused as to the precise difference between these. Do they not perform the same operation? Is there any situations in which one would be preferred over another?
2. Second, in order to control for correlated effect sizes and correlated sampling variance in my own dataset, I will need to produce a variance-covariance matrix for my data using the impute_covariance_matrix() function in clubsandwich, which will then be fed into a multilevel model (effect sizes nested within studies) specified in the metafor function rma.mv().
My question here concerns the "smooth_vi" input of the impute_covariance_matrix() function. I am a little unclear as to its use. The help page specifies "If smooth_vi = TRUE, then all of the variances within cluster j will be set equal to the average variance of cluster j".
I interpreted this as though it is simply removing variance within clusters (i.e. studies) via averaging, which I suspect would be inappropriate for a multi-level meta-analysis in which we would want to capture that variance - indeed, is this not the reason we specify a multilevel structure in the first place? What is confusing to me is the only example code I have seen online appears to set smooth_VI to true when specifying a multi-level model (in which effects are nested within studies), so I am a little lost.
Once again, any help on the above is greatly appreciated!
Brendan
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