If you want to know if your model fit will your data, then looking at
residual-type plots is useful, as can be plotting the model-predictions and
observed data together.  You might also find interesting "R2 statistics for
mixed models" by Matthew Kramer.  Beware--as others have indicated, there
is no widely-accepted measure of R2 for mixed models.

Kevin


On Mon, Apr 30, 2012 at 5:21 AM, klair87@libero.it <klair87@libero.it>wrote:

> Goodmorning everybody,
> i'm an italian statistician and i'm using R for research.
>
> Could someone tell me some indices to see the goodness of fit in multilevel
> modelling?
> I'm using the lmer function, and I want to know if my model fit well my
> data.
> I actually want to justify the use of multilevel model instead the
> classical
> one.
>
> Hope someone can help me.
> Thank you.
>
> Greetings
> Chiara
>
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> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Kevin Wright

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