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 > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. Dr. Hank Stevens, Associate Professor 338 Pearson Hall Botany Department Miami University Oxford, OH 45056 Office: (513) 529-4206 Lab: (513) 529-4262 FAX: (513) 529-4243 http://www.cas.muohio.edu/~stevenmh/ http://www.muohio.edu/ecology/ http://www.muohio.edu/botany/ "E Pluribus Unum" ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
