Dear Sacha,
Do you revisit the same locations per site? If so, use (1|site/location) as
random effect. Otherwise use just (1|site). You might want to add a crossed
random effect (1|date) if you can expect an effect of phenology.
Best regards,
Thierry
PS R-sig-mixed-models is a better list for this kind of questions.
----------------------------------------------------------------------------
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 Sacha Viquerat
> Verzonden: vrijdag 25 februari 2011 13:16
> Aan: r-help
> Onderwerp: [R] count data
>
> hello dear list! I wonder about the layout of my csv for my
> study design:
>
> i have 11 different sites.
>
> each site had been visited 9 times.
>
> on each visit, 6 distinctive water parameters had been taken
> ONCE on each visit (as continuous variables).
>
> on each visit, the fish abundance was counted using a net at
> 3 different locations within the site (count data).
>
> I know i will have to do an lmer using the nested locations
> as error term. Question is: how to organize my data, since i
> have abundances from the same 3 locations per site replicate
> but only one water parameter measurement per site replicate.
> to give you an idea, heres the basic look so far of my csv:
>
>
> site location abundance pH no3 and so on...
> A 1 12 7.1 0.003 ...
> A 2 15 7.1 0.003 ...
> A 3 18 7.1 0.003 ...
> B 1 11 7.4 0.004 ...
> B 2 8 7.4 0.004 ...
> B 3 17 7.4 0.004 ...
> A 1 13 7.2 0.001 ...
> A 2 19 7.2 0.001 ...
> A 3 21 7.2 0.001 ...
> B 1 9 6.9 0.002 ...
> B 2 5 6.9 0.002 ...
> B 3 2 6.9 0.002 ...
>
> i just made up the table to give an idea how the data looks
> like. the goal would be to analyze fish abundance ~ water
> parameters, does anyone have a suggestion?
>
> thanks in advance!
>
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