[R-sig-ME] modeling the effect of grass height on insect biomass

[Joaquín Aldabe]

Thankyou very much Thierry.
All the best,
Joaquín

2015-10-05 10:31 GMT-02:00 Thierry Onkelinx <thierry.onkelinx at inbo.be>:

> Dear Joaquin,
>
> Please keep the mailinglist in cc.
>
> I'd rather think of the weeks being crossed with the fields than nested.
> E.g. the effect of a week is probably similar on all fields. Then the model
> looks like biomas~grass height +(1|Site/Field) + (1|Week). Note that
> you'll need lme4 to fit that. crossed random effects are to straightforward
> in nlme.
>
> Random effects with as little as 4 or 5 levels might have unreliable
> variance estimates. Keep that in mind when examining the modeloutput.
>
> Best regards,
>
> 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
>
> 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
>
> 2015-10-05 14:00 GMT+02:00 Joaquín Aldabe <joaquin.aldabe at gmail.com>:
>
>> Thanks Thierry. Acutually, I collected each trap once a week, but decided
>> to sum the the whole content (30 days). Should I conserve the weekly
>> sampling? if so I guess the model could be insect biomas~grass height
>> +(1|Site\Field\Week) ?
>> Thanks again.
>> Joaquín.
>>
>> 2015-10-05 9:40 GMT-02:00 Thierry Onkelinx <thierry.onkelinx at inbo.be>:
>>
>>> Dear Joaquin
>>>
>>> Your model seems reasonable, assuming that you measure the pitfalls only
>>> once.
>>>
>>> Best regards,
>>>
>>> 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
>>>
>>> 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
>>>
>>> 2015-10-05 13:22 GMT+02:00 Joaquín Aldabe <joaquin.aldabe at gmail.com>:
>>>
>>>> Dear all, I want to see the effect of grass height on insect biomass in
>>>> a
>>>> farm close to a coastal lagoon in Uruguay. For that I chose 5 pairs of
>>>> fields. Each pair consist on a field with tall grass and the other with
>>>> short grass. Each pair of fields are close to each other, in order to
>>>> reduce the effect of soil type and other confounding variables. In each
>>>> field I installed 6 pitfall traps, separated 100 m each. I collected
>>>> insects for 30 days.
>>>>
>>>> Is the following modeling approach correct?: I called Site to each field
>>>> pair (as they are geographically separated)
>>>>
>>>> model=lme(insect biomass~grass height + (1|Site\Field), data)
>>>>
>>>> Alternatively I thought of doing paired t-test..
>>>>
>>>> Thankyou very much for your help.
>>>>
>>>> Joaquín.
>>>>
>>>> --
>>>> *Joaquín Aldabe*
>>>>
>>>> *Grupo Biodiversidad, Ambiente y Sociedad*
>>>> Centro Universitario de la Región Este, Universidad de la República
>>>> Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha
>>>>
>>>> *Departamento de Conservación*
>>>> Aves Uruguay
>>>> BirdLife International
>>>> Canelones 1164, Montevideo
>>>>
>>>> https://sites.google.com/site/joaquin.aldabe
>>>> <https://sites.google.com/site/perfilprofesionaljoaquinaldabe>
>>>>
>>>>         [[alternative HTML version deleted]]
>>>>
>>>> _______________________________________________
>>>> R-sig-mixed-models at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
>>>>
>>>
>>>
>>
>>
>> --
>> *Joaquín Aldabe*
>>
>> *Grupo Biodiversidad, Ambiente y Sociedad*
>> Centro Universitario de la Región Este, Universidad de la República
>> Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha
>>
>> *Departamento de Conservación*
>> Aves Uruguay
>> BirdLife International
>> Canelones 1164, Montevideo
>>
>> https://sites.google.com/site/joaquin.aldabe
>> <https://sites.google.com/site/perfilprofesionaljoaquinaldabe>
>>
>>
>


-- 
*Joaquín Aldabe*

*Grupo Biodiversidad, Ambiente y Sociedad*
Centro Universitario de la Región Este, Universidad de la República
Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha

*Departamento de Conservación*
Aves Uruguay
BirdLife International
Canelones 1164, Montevideo

https://sites.google.com/site/joaquin.aldabe
<https://sites.google.com/site/perfilprofesionaljoaquinaldabe>

	[[alternative HTML version deleted]]