Dear group,

I have been advised that I need to use penalised iteratively reweighted least squares (PIRLS) to improve some of my lmer models, rather than my current REML approach.

I have spent a fair bit of time using mixed models but this is new to me, I was wondering if someone could explain whether this can be implemented in or on top of lme4, if there is a package to do so, or if I need to code manually.
Also, why and how this is an improvement.

The purpose of our models is to build patient-specific growth curves and then use these models to predict a new patient's growth and then improve this model after some observations have been made.

I have been going through Douglas Bates' paper on theory of mixed models http://cran.r-project.org/web/packages/lme4/vignettes/Theory.pdf

But must say I am a little lost as my maths isn't up to scratch.


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