Thanks to all!I've a question about my model explication. I consider time as a factor variable thus my desgin seems to look like a splitplot design, in which time is a kind of treatment.From an old post ..."In my design I have 48 permanent plots in 3 summits (16 plots for each summit). Plots are grouped in clusters arranged in the cardinal direction (4 plots for cardinal direction = 16 plots) and grouped into summits (16 plots for summit x 3 summits = 48 plots). I have two observations of the response variable for each plot: 2001 and 2012. The response variable is a vegetation indicator S. Plots are nested into cardinal direction and summits (plots are nested within the combinations of summit and direction?)I 'd like to test if the vegetation indicator S is changed over time"...
I think that the difference between a classical spliplot desing and my design is that both summits (Blocks) and directions (plots) as suggested by Philip Tom, are fixed effect and plots (subplot in a splitplot design) are nested within the intercation of summits and directions. Moreover I need to take into account that I have two repated measure on the same plot (subplots).
                                                                                                                                
Ludovico
Frate

PhD student (University of Molise - Italy)
Environmetrics Lab
http://www.distat.unimol.it/STAT/environmetrica/organico/collaboratori/ludovico-frate-1
Department of Biosciences and Territory - DiBT
Università del Molise.
Contrada Fonte
Lappone, 
86090 -  Pesche (IS)
ITALIA.
Cel: ++39
3333767557
Fax: ++39 (0874) 404123
E-mail ludovico.frate@unimol.it
ludovicofrate@hotmail.it


> From: Thierry.ONKELINX@inbo.be
> To: ludovicofrate@hotmail.it; r-sig-mixed-models@r-project.org
> Subject: RE: [R-sig-ME] longitudinal data/repeated measure
> Date: Thu, 4 Apr 2013 08:24:09 +0000
> 
> Dear Ludovico,
> 
> Use time as a factor.
> 
> Best regards,
> 
> Thierry
> 
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
> + 32 2 525 02 51
> + 32 54 43 61 85
> Thierry.Onkelinx@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@r-project.org [mailto:r-sig-mixed-models-bounces@r-project.org] Namens Ludovico Frate
> Verzonden: woensdag 3 april 2013 16:28
> Aan: r-sig-mixed-models@r-project.org
> Onderwerp: [R-sig-ME] longitudinal data/repeated measure
> 
> Hi there,I need advice in longitudinal data/repeated measure analysis. In particular, I have some difficults about the fixed effect of time in these type of studies. With only two repeated measures, taken on the same subject two times (2001 and 2012) and if I want to detect if the response variable is different between the two measures  (2001 and 2012), how should I treat the time effect? As a continuos variable or a grouping factor?The measure were taken in 2001 and in 2012. If I explicit time as a continuous variable the model (linear mixed model) doesn't reach the convergence, because in this case, the intercept represent the measurement at time 0. Perhaps I should assign the value of 0 and 11 respectively to 2001 and 2012, or treat time as a grouping factor (time a and time b)?Thanks in advanceLudovico
> 
> Ludovico
> Frate
> 
> PhD student (University of Molise - Italy) Environmetrics Lab
> http://www.distat.unimol.it/STAT/environmetrica/organico/collaboratori/ludovico-frate-1
> Department of Biosciences and Territory - DiBT Università del Molise.
> Contrada Fonte
> Lappone,
> 86090 -  Pesche (IS)
> ITALIA.
> Cel: ++39
> 3333767557
> Fax: ++39 (0874) 404123
> E-mail ludovico.frate@unimol.it
> ludovicofrate@hotmail.it
> 
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