
Hi Ben!

First I thank you for your attention. Unfortunately, the ANOVA does not work with vglm. In
another email, Rafael warned me that actually a lot of zeros does not
necessarily imply a distribution of zeros binomail inflated. So how could I test if my variable is or not a binomial zero inflated?

Thanks.

 
M.Sc Ivan Bezerra Allaman 
Zootecnista
Doutorando em Produção Animal/Aquicultura - UFLA 
email e msn - ivanalaman@yahoo.com.br 
Tel: (35)3826-6608/9925-6428




________________________________
De: Ben Bolker [via R] <ml-node+2221578-2039137178-109182@n4.nabble.com>

Enviadas: Terça-feira, 18 de Maio de 2010 13:34:01
Assunto: Re: Using the zero-inflated binomial in experimental designs

 Ivan Allaman <ivanalaman <at> yahoo.com.br> writes: 


> 
> 
> I'm trying to use the inflated binomial distribution of zeros (since 75% of 
> the values are zeros) in a randomized block experiment with four 
> quantitative treatments (0, 0.5, 1, 1.5), but I'm finding it difficult, 
> since the examples available in VGAM packages like for example, leave us
> unsure of how it should be the data.frame for such analysis. Unfortunately 
> the function glm does not have an option to place a family of this kind I'm 
> about, because if I had, it would be easy, made that my goal is simple, just 
> wanting to compare the treatments. For that you have an idea, here is an
> example of my database. 
> 
> BLOCK		NIV  	       NT	        MUMI 
> Inicial		0	       18	          0 
[snip] 

> 
> where: NIV are the treatments; NT is the total number of piglets born; Mumi 
> is the number of mummified piglets NT. Mumi The variable is of interest. If 
> someone can tell me some stuff on how I can do these tests in R, similar to 
> what I would do using the function glm, I'd be grateful. 
> I thank everyone's attention. 

something like comparing the likelihoods of 

m1 <- vglm(cbind(MUMI,NT-MUMI)~NIV*BLOCK,zibinomial,data=mydata) 
m2 <- vglm(cbind(MUMI,NT-MUMI)~NIV+BLOCK,zibinomial,data=mydata) 
m3 <- vglm(cbind(MUMI,NT-MUMI)~BLOCK,zibinomial,data=mydata) 

I don't know whether the anova() method works for VGLM objects 
or not. 

  By the way, 75% zeroes doesn't necessarily imply zero-inflation -- 
perhaps it just means a low incidence? 

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