Hi Kendra,
>> I am trying to figure out how to apply a loglog link to a binomial
>> model (dichotomous response variable with far more zeros than ones).
If I were you I would look at ?zeroinfl in package pscl.
Regards, Mark.
Kendra Walker wrote:
>
>
>
> I am trying to figure out how to apply a loglog link to a binomial
> model (dichotomous response variable with far more zeros than ones).
> I am aware that there are several relevant posts on this list, but I
> am afraid I need a little more help. The two suggested approaches
> seem to be: 1) modify the make.link function in GLM, or 2) use the
> loglog or cloglog functions in the VGAM package. Below are my
> questions for each. Responses to either are much appreciated.
>
> 1) Modifying the make.link function:
> In his Sat, 24 Jan 2009 post, Re: [R] glm binomial loglog (NOT
> cloglog) link, William Simpson suggested a loglog={} insertion that
> seems reasonable. Being new to R, however, I am going in circles
> trying to figure out make this seemingly simple modification to the
> code. If anyone has the patience to step me through the process, or
> refer me to the relevant information, I would be very grateful.
>
> 2) Using the loglog function in VGAM:
> I tried fitting the model: m<- vglm(Y~X,
> family=binomialff(link="loglog"), data = d) but I get the following
> error? Error in lm.fit(X_vlm, z_vlm, ...) : NA/NaN/Inf in foreign
> function call (arg 4) In addition: Warning message:In log(log(theta))
> : NaNs produced?.
> If I run the same model using cloglog as the link, I get a result that
> looks like the result I get using cloglog in GLM. This is a bad fit
> for my data, however, as I have many more zeros than ones. The help
> document for loglog states that NaNs are produced when theta is close
> to 1 unless earg is used. I am confused as to how to properly use the
> earg parameter (and why I do not need it for cloglog despite having
> many zeros), leading me to wonder whether the loglog link here is
> really what I think it is (the compliment of cloglog). Again, any
> insights as to what I am missing would be appreciated.
>
> Many thanks,
>
>
> Kendra Walker,
> School of Natural Resources and the Environment,
> University of Michigan
>
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