[R-sig-ME] false convergence glmer when quadratic terms are included

ONKELINX, Thierry Thierry.ONKELINX at inbo.be
Tue May 19 12:32:09 CEST 2009

Dear Stijn,

Why don't you use poly(x, 2) instead? Adding x^2 with large or small
values will lead to even larger or smaller values. That may cause the
model to become unstable. Poly(x, 2) will avoid that by rescaling.




ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be

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-----Oorspronkelijk bericht-----
Van: r-sig-mixed-models-bounces at r-project.org
[mailto:r-sig-mixed-models-bounces at r-project.org] Namens Stijn Ruiter
Verzonden: dinsdag 19 mei 2009 12:18
Aan: r-sig-mixed-models at r-project.org
Onderwerp: [R-sig-ME] false convergence glmer when quadratic terms are

Dear all,
Somehow I always get false convergence warnings when including a
quadratic term in a glmer equation. With lmer I have no such problems.
So, my guess is that this has to do with the different algorithm used
for glmer models.
The following example model (which can easily be estimated in
alternative mixed effects programs such as MLwiN or HLM) result in


It leads to:
Warning message:
In mer_finalize(ans) : false convergence (8)

What is the problem here? Why these convergence issues?


Best regards,

Stijn Ruiter
Department of Sociology / ICS
Radboud University Nijmegen
P.O. Box 9104
6500 HE Nijmegen

Phone: + 31 24 361 2272
Fax:   + 31 24 361 2399

Visiting address:
Thomas van Aquinostraat 4.01.71

website: http://oase.uci.ru.nl/~sruiter

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