genZcor

Description

constructs the design matrix for the correlation structures: independence, echangeable, ar1 and unstructured The user will need this function only as a basis to construct a user defined correlation structure: use genZcor to get the design matrix Z for the unstructured correlation and define the specific correlation structure by linear combinations of the columns of Z.

Usage

genZcor(clusz, waves, corstrv)

Arguments

Value

Author(s)

Jun Yan jyan.stat@gmail.com

See Also

fixed2Zcor

Examples

#example to construct a Toeplitz correlation structure
#    sigma_ij=sigma_|i-j|

#data set with 5 clusters and maximally 4 observations (visits) per cluster
 gendat <- function() {
       id <- gl(5, 4, 20)
       visit <- rep(1:4, 5)
       y <- rnorm(id)
       dat <- data.frame(y, id, visit)[c(-2,-9),]
}

set.seed(88)
dat<-gendat()

#generating the design matrix for the unstructured correlation
zcor <- genZcor(clusz = table(dat$id), waves = dat$visit, corstrv=4)
# defining the Toeplitz structure 
zcor.toep<-matrix(NA, nrow(zcor),3)
zcor.toep[,1]<-apply(zcor[,c(1,4,6)],1,sum)
zcor.toep[,2]<-apply(zcor[,c(2,5)],1,sum)
zcor.toep[,3]<-zcor[,3]

zfit1 <- geese(y ~ 1,id = id, data = dat,
                   corstr = "userdefined", zcor = zcor.toep)


zfit2 <- geeglm(y ~ 1,id = id, data = dat,
                   corstr = "userdefined", zcor = zcor.toep)

Results