FYI, I think Lucia is referring to advice such as this:
http://davidhughjones.blogspot.com/2009/11/lme-false-convergence.html
I can't speak to whether this actually does or does not help, but I guess the idea is that convergence may be helped if there are not any very small or very large values of the parameters being estimated.
Jake




Jake....ahh...I see. The danger with that type of advice is that the 'must divide by 100' becomes a rule of thumb. I would
recommend to standardize continuous covariates in case of numerical problems, or scale them between 0 and 1 (ranging). Or convert meters in
kilometers, which means divide by 1000..:-). The later one certainly avoids problems in varPower and varExp stuff.

Yes..it does help!

Alain



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Dr. Alain F. Zuur
First author of:

1. Analysing Ecological Data (2007).
Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p.
URL: www.springer.com/0-387-45967-7


2. Mixed effects models and extensions in ecology with R. (2009).
Zuur, AF, Ieno, EN, Walker, N, Saveliev, AA, and Smith, GM. Springer.
http://www.springer.com/life+sci/ecology/book/978-0-387-87457-9


3. A Beginner's Guide to R (2009).
Zuur, AF, Ieno, EN, Meesters, EHWG. Springer
http://www.springer.com/statistics/computational/book/978-0-387-93836-3


4. Zero Inflated Models and Generalized Linear Mixed Models with R. (2012) Zuur, Saveliev, Ieno.
http://www.highstat.com/book4.htm

Other books: http://www.highstat.com/books.htm


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