HR {SASmixed}

Heart rates of patients on different drug treatments

Description

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

Format

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

Source

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).

Examples

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))
}