[R] nested, repeated measure lme

[ONKELINX, Thierry]

Dear Christoph,

Why should (1) not work? As long as you have enough levels, it should
not be a problem. You need at least 6 levels for each random effect.
When you have less than six levels, then you better move those variables
to the fixed effects.

An example: 2 blocks with each 2 plots. Each plot has 2 subplots. A
subplot contains 8 individuals.
In this case you have 2 blocks, 4 plots, 8 subplots and 64 individuals.
So the model will look like: 
y~explanatory.variables + block/plot, random=~time|subplot/individual

Another example: 6 blocks with each 2 plots. Each plot has 2 subplots. A
subplot contains 3 individuals.
In this case you have 6 blocks, 12 plots, 24 subplots and 72
individuals. So the model will look like: 
y~explanatory.variables, random=~time|block/plot/subplot/individual

HTH,

Thierry

------------------------------------------------------------------------
----
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
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 Christoph Scherber
Verzonden: donderdag 20 augustus 2009 11:33
Aan: r-help at stat.math.ethz.ch
Onderwerp: [R] nested, repeated measure lme

Dear all,

Suppose I have a nested, repeated measure lme model. Which of the
following formulae is  correct?
(assuming data are sampled from several plots in an agricultural
experiment)

(1) y~explanatory.variables,random=~time|block/plot/subplot/individual
(2) y~explanatory.variables,random=~time|unique.ID.of.every.individual

I have read that (2) is the only approach that works. But how could I
then still include the nesting information from (1)?

Many thanks for your help!

Best wishes
Christoph


(using R 2.9.0 and the nlme library on Windows XP)




--
Dr. rer.nat. Christoph Scherber
University of Goettingen
DNPW, Agroecology
Waldweg 26
D-37073 Goettingen
Germany

phone +49 (0)551 39 8807
fax   +49 (0)551 39 8806

Homepage http://www.gwdg.de/~cscherb1

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