[R] Error message when using zero-inflated count regression model in package zicounts

[Hank Stevens]

Hi Jim,
Two thoughts come to me, unencumbered by the thought process or  
knowledge of zicounts:
1. Is Poisson really NOT appropriate? (do you have to use zicounts?)
2. Are you 110% certain that all variables are the same length? Would  
NA's interfere?
Cheers,
Hank
On Aug 13, 2007, at 5:10 PM, James Milks wrote:

> I have data on number of vines per tree for ~550 trees.  Over half of
> the trees did not have any vines and the data is fairly skewed
> (median = 0, mean = 1.158, 3rd qu. = 1.000).  I am attempting to
> investigate whether plot location (four sites), species (I'm using
> only the four most common species), or tree dbh has a significant
> influence on the number of vines per tree.  When I attempted to use
> the zicounts function, R gave me the following error message:
>
>> vines.zip<-zicounts(resp=Total.vines~.,x=~Site+Species+DBH,z=~Site
> +Species+DBH,distrname="ZIP",data=sycamores.1)
> Error in ifelse(y == 0, 1, y/mu) : dim<- : dims [product 12] do not
> match the length of object [549]
> In addition: Warning messages:
> 1: longer object length
>         is not a multiple of shorter object length in: x[good, ] * w
> 2: longer object length
>         is not a multiple of shorter object length in: eta + offset
> 3: longer object length
>         is not a multiple of shorter object length in: y/mu
>
> I do not know enough about the calculations done in the function to
> interpret the error messages.  Is there a glitch in my data and if
> yes, what is it?
>
> Thanks for your help.
>
> Jim Milks
>
> Graduate Student
> Environmental Sciences Ph.D. Program
> 136 Biological Sciences
> Wright State University
> 3640 Colonel Glenn Hwy
> Dayton, OH 45435
>
>
>
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>
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Dr. Hank Stevens, Associate Professor
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Botany Department
Miami University
Oxford, OH 45056

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