In the evaluation of drugs for possible clinical application, studies are routinely performed on rodents. For a particular study drawn from the statistical literature, suppose the immediate aim is to estimate theta, the probability of tumor in a population of female laboratory rats of type 'F344' that receive a zero dose of the drug — a control group. This gives data from historical control groups, and one current experimental control group.
A data frame with 71 observations on the following 3 variables.
number of rats with tumors
number of rats in experiment
a factor with levels
1 2 3 4 5 6 7
data(rats) summary(rats) # moment estimate of (alfa, beta) in beta distribution is (1.4, 8.6) with(subset(rats, Current=="0"), hist( y/N, freq=FALSE)) plot(function(x) dbeta(x, 1.4, 8.6), from=0, to=1, col="red", add=TRUE) # plotting posterior in same plot: plot(function(x) dbeta(x, 5.4, 18.6), from=0, to=1, col="blue", add=TRUE)