Re: [R] what does this warnings mean? and what should I do?

From: Berton Gunter <gunter.berton_at_gene.com>
Date: Tue 20 Dec 2005 - 04:48:17 EST


 Spencer:

(warning: highly biased, personal opinions)

My $.02
> Looking now at your output, I notice that "Corr" between
> "(Intercept)" and "trust.cz1" for the "Random Effects" "commid" is
> 1.000. This says that the structure of your data are not adequate to
> allow you to distinguish between random effects for "(Intercept)" and
> "trust.cz1" for "commid", while simultaneously estimating all
> the fixed
> effects you have in the model.

Quite right. Design is the cause; overfitting/identifiability is the symptom.
>
> If I were you, I'd start be deleting all the terms
> from the model
> that don't have a "Signif. code" beside it in the table of "Fixed
> effects" and then refit the smaller model, preferably also using
> 'method="AGQ"'.

Well, this might work, but it's also a prescription for overfitting a highly biased model.

What he really needs to do is carefully rethink. What is a parsimonious model given the data at hand? Unfortunately, this is far from a trivial issue. Model choice for nonlinear model fitting is conceptually and statistically difficult.

IMHO, the tendency to overfit mechanistically motivated models with insufficient, poorly designed data is a ubiquitous scientific practice, rarely understood by scientists (due to the complexity). As a result, there are a lot of questionable results published in peer-reviewed literature. Eventually it gets sorted out, but it can take a while. See Kuhn and Feyerabend, for example.

Always enjoy your comments. Keep 'em coming.


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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Dec 20 05:00:48 2005

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