[R-meta] Nonlinear meta-regression

[Michael Dewey]

Dear César

I would have to say that based purely on the plot and given the sparsity 
of points for high levels of phosphorus I would not see quite what you 
see. However if on theoretical grounds you are expecting a ceiling then 
fine.

If you want to fit a model which is non-linear in the variables then you 
just enter the transformed predictors as moderators. So this would apply 
if you wanted a polynomial or splines ir some form of segmented fit for 
phosphorus. If you want a model which is non-linear in the parameters 
like some form of exponential then that lies outside what I know how to 
do but someone else will doubtless chip in.

Michael

On 18/12/2018 08:54, Cesar Terrer Moreno wrote:
> Dear all,
> 
> The studies of my meta-analysis form this relationship, with y as the effect size, x as the main moderator, and the size of points as the inverse of the variance: https://imgur.com/a/ad6Br5y <https://imgur.com/a/ad6Br5y>
> 
> In my opinion, the regression is clearly nonlinear. And in ecological terms, it makes sense that the relationship saturates. Here I’ve just fitted a regular loess function to aid the eye in seeing the pattern I refer to.
> 
> How would you fit a nonelinear mixed-effects meta regression with metafor for a case like this?
> 
> Thanks in advance.
> Best,
> César
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> 
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html