[R-sig-eco] Question about poisson GLM

[Rob Robinson]

Rox
 If anno is year and year is 2000:2010 (or whatever) and you have a
negative relationship then extending this back to 0 (the intercept) will
yield quite a large number (2000*0.07=140 for instance). Does coding year
as year of study (1:10) or even (-4:5), if you wanted the intercept to be
in the middle of your study period, help?
cheers
rob


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Dr Rob Robinson, Principal Ecologist
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====== "How can anyone be enlightened, when truth is so poorly lit" =======


On 27 October 2014 14:38, rosanna di maggio <rosannadimaggio at gmail.com>
wrote:

> Dear all,
>
> I'm trying to perform a poisson GLM with lme4 using the number of
> individuals as dependent variable and i) years of study and ii) different
> study areas as factors... So far so good..
>
> But the results are quite curious...  The estimates and standard errors are
> huge.. Is is normal? I don't think so...
>
>
> This is an example of what happen:
>
>
> Call:
> glm(formula = NTOT ~ areaN * anno, family = poisson)
>
> Deviance Residuals:
>     Min       1Q   Median       3Q      Max
> -3.7465  -1.0629  -0.5000   0.3132   6.8188
>
> Coefficients:
>               Estimate Std. Error z value Pr(>|z|)
> (Intercept) 140.786646  27.766187   5.070 3.97e-07 ***
> areaN        71.479294  11.876992   6.018 1.76e-09 ***
> anno         -0.069199   0.013823  -5.006 5.56e-07 ***
> areaN:anno   -0.035572   0.005912  -6.017 1.78e-09 ***
>
>
>
>
> I cannot understand the reason of these results... Someone can help me?
>
>
>
> Thank you
>
> Rox
>
> --
> Rosanna Di Maggio,PhD student,
> Laboratorio di Zoogeografia ed Ecologia Animale (LABZEA)
> Dipartimento Scienze e Tecnologie Biologiche, Chimiche e Famaceutiche
> (STEBICEF)
> Universita'  di  Palermo, Via Archirafi 18 - 90123 Palermo (I)
> Mobile: +393290842994
> Email 2: rosanna.dimaggio01@ <rosannadimaggio at gmail.com>unipa.it
> Website: www.researchgate.net/profile/Rosanna_Di_Maggio?ev=prf_highl
>
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>
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