Dear Ben,
Maybe the model converges more slowy than other models. Running more iterations
might solve the problem. Have a look at ?lme and ?lmeControl.
Best regards,
Thierry
PS R-sig-mixedmodels is a better list for questions on lme().
----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium
Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be
To call in the statistician after the experiment is done may be no more than
asking him to perform a post-mortem examination: he may be able to say what the
experiment died of.
~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data.
~ Roger Brinner
The combination of some data and an aching desire for an answer does not ensure
that a reasonable answer can be extracted from a given body of data.
~ John Tukey
> -----Oorspronkelijk bericht-----
> Van: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org]
> Namens Ben Grannan
> Verzonden: maandag 25 juli 2011 23:00
> Aan: r-help at r-project.org
> Onderwerp: [R] lme convergence error
>
> Hello, I am working from a linux 64 machine on a server with R-2.12 (I
can't
> update to 2.13). I am iterating through many linear mixed models for
> longitudinal data and I occasionally receive the following convergence
> error:
>
> > BI.lme <- lme(cd4 ~ time + genBI + genBI:time + C1 + C2 + C11 +
C12,
> random =~ 1 + time | IID, data = d)
>
> Error in lme.formula(cd4 ~ time + genBI + genBI:time + PC1 + :
> nlminb problem, convergence error code = 1
> message = false convergence (8)
>
> >From iteration to iteration, genBI is the only variable which changes
> >and it
> is a numerical variable equal to 1, 2, or 3 for a given IID. When I remove
the
> interaction term genBI:cd4years there is no problem with convergence.
> Also, I have played around with scaling time (days to years, eg) which can
solve
> the problem but then leads to convergence issues in other iterations.
> When I shift the time (say in units of years by +2) the model also
converges. So
> it seems like the genBI:time is the issue. Do you have any suggestions for
> exploring why I get these convergence errors only on certain iterations? I
really
> appreciate any suggestions!
>
> Ben
>
> Here is a summary of the included variables just in case it is helpful:
>
> IID (808 groups) cd4 time ( in years)
> C1
> ACTG_617 : 26 Min. : 0.0 Min. :0.0000 Min. :-0.032700
> ACTG_1055: 25 1st Qu.: 288.0 1st Qu.:0.4603 1st Qu.: 0.001600
> ACTG_1590: 25 Median : 434.0 Median :1.1534 Median : 0.004300
> ACTG_200 : 23 Mean : 461.3 Mean :1.2107 Mean : 0.002139
> ACTG_420 : 23 3rd Qu.: 599.0 3rd Qu.:1.8630 3rd Qu.: 0.006100
> ACTG_454 : 23 Max. :2022.0 Max. :2.7808 Max. : 0.011300
> (Other) :11992
>
> C2 C11 C12
> Sex
> Min. :-0.105800 Min. :0.000 Min. :0.0000 Min. :1.000
> 1st Qu.: 0.002100 1st Qu.:0.000 1st Qu.:0.0000 1st Qu.:1.000
> Median : 0.007900 Median :0.000 Median :0.0000 Median :1.000
> Mean : 0.001803 Mean :0.367 Mean :0.3020 Mean :1.095
> 3rd Qu.: 0.011700 3rd Qu.:1.000 3rd Qu.:1.0000 3rd Qu.:1.000
> Max. : 0.030800 Max. :1.000 Max. :1.0000 Max. :2.000
>
> genBI
> Min. :1.000
> 1st Qu.:1.000
> Median :1.000
> Mean :1.369
> 3rd Qu.:2.000
> Max. :3.000
>
> [[alternative HTML version deleted]]
>
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