[R-sig-ME] interaction terms interpretation

[Ben Bolker]

Consider taking a look at
http://ms.mcmaster.ca/~bolker/R/misc/foxchapter/bolker_chap.html .

On Mon, Aug 10, 2015 at 10:30 AM, Joaquín Aldabe
<joaquin.aldabe at gmail.com> wrote:
> Thankyoy very much Ken and Thierry. I'll try that. Is there any specific
> function for making graphs of the model? I appreciate recommendations or
> citations to explore how to graph model results. Thanks again. Joaquin
> El 10/08/2015 07:36, "Ken Beath" <ken.beath at mq.edu.au> escribió:
>
>> There is actually a continuous third order interaction, which are just
>> about impossible to interpret.
>>
>> As well as the graphs, which you always should start with, think about
>> what is sensible for the model. Should any of the predictors be log-scaled?
>> As AMGP is a count it wouldn't be surprising it it is, or use log(1+x) if
>> there are zeroes.
>>
>> Look at diagnostic plots and make sure that everything is fine, especially
>> that there are no outliers which might be causing the interaction.
>>
>> Ken
>>
>> On 10 August 2015 at 17:02, Thierry Onkelinx <thierry.onkelinx at inbo.be>
>> wrote:
>>
>>> Dear Joaquin,
>>>
>>> Your mail is mangled because you send it in HTML. This makes the model
>>> output very hard to read.
>>>
>>> It's impossible to interpret model output without thorough knowledge of
>>> the
>>> dataset. I suggest that you try to make some graphs of the model.
>>>
>>> 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
>>>
>>> 2015-08-07 21:27 GMT+02:00 Joaquín Aldabe <joaquin.aldabe at gmail.com>:
>>>
>>> > Hi all, I´m running a mixed model with poisson error distribution as I
>>> have
>>> > count data of a shorebird species. My predictors are AMGP (another
>>> > shorebird that is usually associated to "my" species and probably has
>>> > ecological influence on it), grass height and field distance to the
>>> lagoon.
>>> >
>>> > I´m having a hard time trying to interpret second order interactions. I
>>> > appreciate your comments of references recommendations. Here is the
>>> output
>>> > of my model. All the best, Joaquín.
>>> >
>>> > Call:glmmadmb(formula = BBSA ~ AMGP * Grass_height *
>>> > Distance_to_lagoon +     (1 | Field_name) + offset(log(Field_area.o)),
>>> > data = my4S,     family = "nbinom1", zeroInflation = TRUE)
>>> > AIC: 226
>>> > Coefficients:                                     Estimate Std. Error
>>> > z value Pr(>|z|)    (Intercept)                           -5.8797
>>> > 1.2250   -4.80  1.6e-06 ***AMGP
>>> > 3.3086     1.0246    3.23   0.0012 ** Grass_height
>>> >      -4.1592     1.9961   -2.08   0.0372 *  Distance_to_lagoon
>>> >            -0.5029     1.3929   -0.36   0.7180    AMGP:Grass_height
>>> >                   2.9442     1.5142    1.94   0.0518 .
>>> > AMGP:Distance_to_lagoon               -2.4695     0.9632   -2.56
>>> > 0.0104 *  Grass_height:Distance_to_lagoon        0.0339     2.0065
>>> > 0.02   0.9865    AMGP:Grass_height:Distance_to_lagoon  -4.0363
>>> > 1.3264   -3.04   0.0023 ** ---Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01
>>> > ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
>>> > Number of observations: total=64, Field_name=16 Random effect
>>> > variance(s):Group=Field_name            Variance StdDev(Intercept)
>>> > 0.03721 0.1929
>>> > Negative binomial dispersion parameter: 20.633 (std. err.:
>>> > 7.4042)Zero-inflation: 1e-06  (std. err.:  6.8336e-09 )
>>> > Log-likelihood: -102
>>> >
>>> >
>>> > --
>>> > *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
>>> >
>>>
>>>         [[alternative HTML version deleted]]
>>>
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>>
>>
>>
>> --
>>
>> *Ken Beath*
>> Lecturer
>> Statistics Department
>> MACQUARIE UNIVERSITY NSW 2109, Australia
>>
>> Phone: +61 (0)2 9850 8516
>>
>> Level 2, AHH
>> http://stat.mq.edu.au/our_staff/staff_-_alphabetical/staff/beath,_ken/
>>
>> CRICOS Provider No 00002J
>> This message is intended for the addressee named and m...{{dropped:12}}
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