Displaying 3 results from an estimated 3 matches for "overdisperion".
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overdispersion
2010 Nov 19
2
Question on overdispersion
I have a few questions relating to overdispersion in a sex ratio data set
that I am working with (note that I already have an analysis with GLMMs for
fixed effects, this is just to estimate dispersion). The response variable
is binomial because nestlings can only be male or female. I have samples of
1-5 nestlings from each nest (individuals within a nest are not independent,
so the response
2010 Jun 02
1
Problems using gamlss to model zero-inflated and overdispersed count data: "the global deviance is increasing"
...ver, most models fail because “the global deviance is increasing” and I am not sure what causes this behaviour. The dataset consists of counts of birds (duck) and 5 habit variables measured in the field (n= 182). The dependent variable (the number of ducks counted)’suffers’ from zero-inflation and overdisperion:
> proportion_non_zero <- (sum(ifelse(data$duck == 0,0,1))/182)
> mean <- mean(data$duck)
> var <- var(data$duck)
> proportion_non_zero
[1] 0.1153846
> mean
[1] 1.906593
> var
[1] 37.35587
(I have no idea how to simulate a zero-inflated overdispersed Poisson variable,...
2010 Oct 07
2
How do I set the dispersion parameter in poisson glm?
Dear R users,
I would like to fit a glm with Poisson distribution and log link with a known dispersion parameter. I do not want to estimate the dispersion parameter. I know what it is, so I simply want to fix it at a constant for this and other models to follow. My simple, no covariate model is:
Tall.glm<-glm(Seedling~1,
family=poisson,
offset(log(area)),
data=tallPSME.df)
I want to