### R packages are so easy to install, even I can do it.  From within R
### I used:
### install.packages("gee", "/home/faculty/gustaf/myRlibs/")
###
### Or to use the package without installing it, the permissions are set
### (I think) so that you can use the library command below from R on unixlab


library(gee, lib.loc="/home/faculty/gustaf/myRlibs/")

### simulate some clustered Poission data (50 clusters of 5 subjects each)

clust.id <- NULL
for (i in 1:50) { clust.id <- c(clust.id, rep(i,5)) }
x <- rnorm(250)
randeff <- rnorm(50,mean=0,sd=log(3))
y <- rpois(250, exp(log(10) + 0.25*x + randeff[clust.id]))

postscript("margmodfig.ps")
plot(clust.id, y)
graphics.off()

### usual glm fit ignoring cluster structure

fit.0 <- glm(y~x, family="poisson")

### marginal model fit with independence working correlation model

fit.1 <- gee(y~x, id=clust.id, family=poisson, corstr="independence")

### marginal model fit with equi-correlated working correlation model

fit.2 <- gee(y~x, id=clust.id, family=poisson, corstr="exchangeable")