HR: Heart rates of patients on different drug treatments
In SASmixed: Data sets from "SAS System for Mixed Models"

Description Format Source Examples

The HR data frame has 120 rows and 5 columns of the heart rates of patients under one of three possible drug treatments.

This data frame contains the following columns:

Patient: an ordered factor indicating the patient.
Drug: the drug treatment - a factor with levels a, b and p where p represents the placebo.
baseHR: the patient's base heart rate
HR: the observed heart rate at different times in the experiment
Time: the time of the observation

Littel, R. C., Milliken, G. A., Stroup, W. W., and Wolfinger, R. D. (1996), SAS System for Mixed Models, SAS Institute (Data Set 3.5).

str(HR)
if (require("lattice", quietly = TRUE, character = TRUE)) {
  xyplot(HR ~ Time | Patient, HR, type = c("g", "p", "r"), aspect = "xy",
         index.cond = function(x, y) coef(lm(y ~ x))[1],
         ylab = "Heart rate (beats/min)")
}
if (require("lme4", quietly = TRUE, character = TRUE)) {
  options(contrasts = c(unordered = "contr.SAS", ordered = "contr.poly"))
  ## linear trend in time
  print(fm1HR <- lmer(HR ~ Time * Drug + baseHR + (Time|Patient), HR))  
  print(anova(fm1HR))
## Not run: 
fm2HR <- update(fm1HR, weights = varPower(0.5)) # use power-of-mean variance
summary(fm2HR)
intervals(fm2HR)             # variance function does not seem significant
anova(fm1HR, fm2HR)         # confirm with likelihood ratio

## End(Not run)
 print(fm3HR <- lmer(HR ~ Time + Drug + baseHR + (Time|Patient), HR))
 print(anova(fm3HR))
 ## remove Drug term
 print(fm4HR <- lmer(HR ~ Time + baseHR + (Time|Patient), HR))
 print(anova(fm4HR))
}