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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