tlc: Subsample (N=100) of data on blood lead levels from the...
In ALA: Data sets and examples for the book "Applied Longitudinal Analysis"

Description Usage Format Details Note Source References Examples

The Treatment of Lead-Exposed Children (TLC) trial was a placebo-controlled, randomized study of succimer (a chelating agent) in children with blood lead levels of 20-44 micrograms/dL.

data(tlc)

A data frame with 400 observations on the following 4 variables.

id: a factor with 100 levels
treatment: a factor with levels placebo and succimer
week: a numeric vector
lead: a numeric vector

These data consist of four repeated measurements of blood lead levels obtained at baseline (or week 0), week 1, week 4, and week 6 on 100 children who were randomly assigned to chelation treatment with succimer or placebo.

Original variable names have been adapted to R conventions. Data were reshaped from wide to long format and the response named lead.

http://biosun1.harvard.edu/~fitzmaur/ala

Treatment of Lead-exposed Children (TLC) Trial Group. (2000). Safety and Efficacy of Succimer in Toddlers with Blood Lead Levels of 20-44 micrograms/dL. Pediatric Research 48:593-599

str(tlc)
summary(tlc)

if (require(lattice)) {
    ## Fig. 6.5 (roughly)
    xyplot(lead ~ week, data=tlc, groups=treatment, type=c("p", "a"),
           cex=0.5,
           xlab="Time (weeks)", ylab="Mean blood lead level (mcg/dL)",
           scales=list(rot=c(0, 1), tck=c(0.5, 0)))
}

if (require(lme4)) {
    tlcNew <- within(tlc, {
        week1 <- ifelse(week > 1, week - 1, 0)
    })
    summary(tlcNew)
    ## Assuming this is the random effect structure used in p. 155
    lmer(lead ~ week + week1 + week:treatment + week1:treatment +
         (week + week1 | id), data=tlcNew)
}