[R-meta] metafor: Categorizing a continuous moderator in random part of rma.mv

[Michael Dewey]

It would seem a bizarre thing to do to me unless it corresponds to some 
scientific question.

Michael

On 14/08/2021 16:59, Luke Martinez wrote:
> 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)?
> 
> Kind regards,
> Luke
> 
> On Sat, Aug 14, 2021 at 6:35 AM Michael Dewey <lists using dewey.myzen.co.uk 
> <mailto:lists using dewey.myzen.co.uk>> wrote:
> 
>     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 if
>      > 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?
> 
>     Michael
> 
>      > Thank you for your clarification,
>      > Luke
>      >
>      >       [[alternative HTML version deleted]]
>      >
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>     Michael
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