Ezzet and Whitehead (1991) analyze data from a two-treatment, two-period crossover trial to compare 2 inhalation devices for delivering the drug salbutamol in 286 asthma patients. Patients were asked to rate the clarity of leaflet instructions accompanying each device, using a 4-point ordinal scale.
inhalerA data frame of 572 observations containing information on the following 5 variables.
The subject number
The rating of the inhaler instructions on a scale ranging from 1 to 4
A contrast to indicate which of the two inhaler devices was used
A contrast to indicate the time of administration
A contrast to indicate possible carry over effects
Ezzet, F., & Whitehead, J. (1991). A random effects model for ordinal responses from a crossover trial. Statistics in Medicine, 10(6), 901-907.
if (FALSE) {
## ordinal regression with family "sratio"
fit1 <- brm(rating ~ treat + period + carry,
data = inhaler, family = sratio(),
prior = set_prior("normal(0,5)"))
summary(fit1)
plot(fit1)
## ordinal regression with family "cumulative"
## and random intercept over subjects
fit2 <- brm(rating ~ treat + period + carry + (1|subject),
data = inhaler, family = cumulative(),
prior = set_prior("normal(0,5)"))
summary(fit2)
plot(fit2)
}