[R-meta] Unimodal relationship?

[Michael Dewey]

Dear Cesar

When you say a unimodal relationship do you mean a U-shaped one? There 
are various options depending on exactly what you want to do.

Michael

On 09/03/2018 12:14, Cesar Terrer Moreno wrote:
> Dear all,
> 
> I initially run a model selection analysis, and found 3 potentially important predictors: MAT, MAP and deltaCO2, and potentially also the interaction MAT:deltaco2: https://www.dropbox.com/s/qeu50krq2e78sju/Rplot11.jpeg?dl=0 <https://www.dropbox.com/s/qeu50krq2e78sju/Rplot11.jpeg?dl=0>
> 
> However, I suspect that the next predictor in importance, CNr, might be more important than here shown. The problem is that it may follow a nonlinear behaviour. In particular, based on the plot, it seems it may follow an unimodal relationship: https://www.dropbox.com/s/ahpq07y8929muti/Rplot13.jpeg?dl=0 <https://www.dropbox.com/s/ahpq07y8929muti/Rplot13.jpeg?dl=0> or at least interact with other predictors more clearly.
> 
> How would you include a potentially unimodal shape in a model in `metafor`?
> 
> This is the best model:
> 
> rma(es, var, data=dat , mods= ~ 1 + MAT + MAP + deltaco2 + deltaco2:MAT, knha=TRUE))
> 
> Please help me figure out how to include CNr in this model as a nonlinear relationship.
> Thanks
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> 
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html