generate variable y to produce excess zero in ZIP analysis

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of S Ellison
Sent: Wednesday, February 20, 2013 8:03 AM
To: lili puspita rahayu; r-help at R-project.org
Subject: Re: [R] generate variable y to produce excess zero in ZIP
analysis

Subject: [R] generate variable y to produce excess zero in
ZIP analysis

Maybe something like

rzip <-  function(n, lambda, zip=0.0) {
	#zip is the desired proportion of _excess_ zeros
               if(zip>1.0 || zip <0) stop("zip must be in (0,1)")
               n.zip <- ceiling(zip*n)
               n.pois <- n-n.zip
              sample( c( rpois(n.pois, lambda), rep(0,n.zip) ) )
}

#Example
rzip(50, 3.5, zip=0.5)

Having said that, I'd bet there's a package out there that already does
it better...

 S Ellison

Dear Mr/Mrs

I am Lili Puspita Rahayu, student from magister third level
of Statistics in Bogor Agriculture University.
Mr/
Mrs, now I'm analyzing the Zero inflated Poisson (ZIP), which
is a solution of the Poisson regression where the response
variable (Y) has zero excess. ZIP now I was doing did not use
real data, but using simulated data in R. Simulations by
generating data on variables x1, x2, x3 with each size n =
100, after which generate data on response variable (Y).
However, when I generate the variable y, after generating
variables x1, x2, x3, then the simulation result in the
variable y that does not have a zero excess. Sometimes just a
coincidence there are 23%, 25% the proportion of zero on the
variable Y. This is because I generate variables x1, x2, x3
with a distribution that has a small parameter values??. I've
been consulting with my lecturer, and suggested to generate
variable Y that can control the proportion of zero on ??ZIP
analysis. I've been trying to make the syntax, but has not
succeeded.I would like to ask for assistance to R to make the
syntax to generate simulated Y variables that can control the
proportion of zeros after generating variables x1, x2, x3 on
ZIP analysis.Thus, I can examine more deeply to determine how
much the proportion of zeros on response variable (Y) that
can be used in the Poisson regression analysis, parametric
ZIP and ZIP semiparametric.

syntax that I made previously by generating variable y
without being controlled to produce zero excess in R :

b0=1.5
b1=-log(2)
b2=log(3)
b3=log(4)
n=100
x1<-rnorm(n, mean=5, sd=2)
x2<-runif(n, min=1, max=2)
x3<-rnorm(n, mean=10, sd=15)

y<-seq(1,n)
for(i in 1:n)

+ {
+ m<-exp(b0+b1*x1[i]+b2*x2[i]+b3*x3[i])
+ yp<-rpois(1,m)
+ y[i]<-yp
+ }


I am very
grateful for the assistance of R.
I am looking forward to hearing from you. Thank you very much.

Sincerely yours
Lili Puspita Rahayu
	[[alternative HTML version deleted]]

*******************************************************************
This email and any attachments are confidential. Any use, copying or
disclosure other than by the intended recipient is unauthorised. If
you have received this message in error, please notify the sender
immediately via +44(0)20 8943 7000 or notify postmaster at lgcgroup.com
and delete this message and any copies from your computer and network.
LGC Limited. Registered in England 2991879.
Registered office: Queens Road, Teddington, Middlesex, TW11 0LY, UK