Jaap: > I have simulated data from a zero-inflated Poisson model, and would like > to use a package like zicounts to test my code of fitting the model. > My question is: can I use zicounts directly with the following simulated > data?
I guess you can use zicounts, but personally I'm more familiar with zeroinfl() from package "pscl" (because I have written this function :)). With that you can easily do: > beta.true<-1.0 > gamma.true<-1.0 > n<-1000 > x<-matrix(rnorm(n),n,1) > pi<-expit(x*beta.true) > mu<-exp(x*gamma.true) > y<-numeric(n) # blank vector > z<-(runif(n)<pi) # logical: T with prob p_i, F otherwise > y[z]<-rpois(sum(z),mu[z]) # draw y_i ~ Poisson(mu_i) where z_i = T > y[!z]<-0 # set y_i = 0 where z_i = F library("pscl") zeroinfl(y ~ 0 + x | 0 + x) which by default fits a ZIP (with log link and logit inflation). hth, Z ______________________________________________ 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.