[R-sig-ME] crossed random effect

[ONKELINX, Thierry]

Dear Cristian,

Having only 2 levels for a random effect is not ideal for a mixed model.
You will get very unreliable variance estiametes. You better fit
observer as fixed effect.
Note that this will only solve the problem of the false convergence. You
will not get good estimates of the inter observer variability because
that will require data on much more observers. 

What is your definition of repetition? Are those 7 different objects
that are measured? Or the same object 7 times?

HTH,

Thierry

------------------------------------------------------------------------
----
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-sig-mixed-models-bounces at r-project.org 
> [mailto:r-sig-mixed-models-bounces at r-project.org] Namens 
> Cristian Pasquaretta
> Verzonden: woensdag 10 november 2010 13:55
> Aan: r-sig-mixed-models at r-project.org
> Onderwerp: [R-sig-ME] crossed random effect
> 
> Dear list,
> 
> I have a really simple problem:
> I want to calculate intra and inter observer variability 
> collecting 7 measures using 2 observers and 2 repetitions for 
> each observer so I build the following model:
> 
> mod=lmer(y~1 +(1|repetition) + (1|observer))
> 
> the y variable is continuous but is completely different for 
> each of the 7 measures.
> the table is:
>                repetition
> observer   1 2 3 4 5 6 7
>             1 2 2 2 2 2 2 2
>             2 2 2 2 2 2 2 2
> but when I run the model the message I get is:
> In mer_finalize(ans) : false convergence (8)
> 
> Can someone help me?
> 
> Thank you
> Cristian
> 
> --
> PhD
> Cristian Pasquaretta
> University of Pavia
> Via Adolfo Ferrata 1,
> 27100 PAVIA
> cristian.pasquaretta at unipv.it
> 
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