fixed2Zcor function

Construct zcor vector

Construct zcor vector (of fixed correlations) from a fixed working correlation matrix, a specification of clusters and a specifcation of waves.

fixed2Zcor(cor.fixed, id, waves)

Arguments

• cor.fixed: Matrix
• id: Clusters
• waves: Vector giving the ordering of observations within clusters.

Returns

A vector which can be passed as the zcor argument to geeglm.

Examples

timeorder <- rep(1:5, 6)
tvar      <- timeorder + rnorm(length(timeorder))
idvar <- rep(1:6, each=5)
uuu   <- rep(rnorm(6), each=5)
yvar  <- 1 + 2*tvar + uuu + rnorm(length(tvar))
simdat <- data.frame(idvar, timeorder, tvar, yvar)
head(simdat,12)

simdatPerm <- simdat[sample(nrow(simdat)),]
simdatPerm <- simdatPerm[order(simdatPerm$idvar),]
head(simdatPerm)

cor.fixed <- matrix(c(1    , 0.5  , 0.25,  0.125, 0.125,
                      0.5  , 1    , 0.25,  0.125, 0.125,
                      0.25 , 0.25 , 1   ,  0.5  , 0.125,
                      0.125, 0.125, 0.5  , 1    , 0.125,
                      0.125, 0.125, 0.125, 0.125, 1     ), nrow=5, ncol=5)
cor.fixed

zcor <- fixed2Zcor(cor.fixed, id=simdatPerm$idvar, waves=simdatPerm$timeorder)
zcor

mod4 <- geeglm(yvar~tvar, id=idvar, data=simdatPerm, corstr="fixed", zcor=zcor)
mod4

See Also

genZcor, geeglm

Author(s)

Søren Højsgaard, sorenh@math.aau.dk