[R-meta] metafor: Categorizing a continuous moderator in random part of rma.mv
m@rt|nez|ukerm @end|ng |rom gm@||@com
Sat Aug 14 17:59:05 CEST 2021
Thanks, Michael. But my question is wouldn't it be ***incongruent*** if I
use the same variable (`count_of_exposure`) as continuous in the fixed part
but as categorical in the random part (at least that congruence is needed
in conventional multilevel models)?
On Sat, Aug 14, 2021 at 6:35 AM Michael Dewey <lists using dewey.myzen.co.uk>
> Comments in-line
> On 14/08/2021 05:53, Luke Martinez wrote:
> > Dear Experts,
> > In metafor's multivariate specification (which gives control over the
> > `struct` argument), apparently there is a requirement for the variable
> > appearing on the left-side of `|` to only be a categorical factor.
> > First, why is this required conceptually?
> Looking at the different options for the struct parameter it is hard to
> see what sense they make for a continuous variable. What dimensions
> would the variance-covariance matrix have?
> > Second, suppose I want to use, say, `count_of_exposure` as a
> > **continuous variable** in the fixed part, then would it be appropriate
> > I use `factor( count_of_exposure) | study` in the random part?
> If converting it into a factor is going to lead to a model which fits
> then it must have relatively few levels otherwise the VCV matrix is
> going to expand uncontrollably. If it has few levels is it useful to fit
> it as continuous rather than as an ordered factor?
> > Thank you for your clarification,
> > Luke
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