Tumor Incidence in Historical Control Groups and Current Group of Rats

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Description

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.

Usage

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Format

A data frame with 71 observations on the following 3 variables.

y

number of rats with tumors

N

number of rats in experiment

Current

a factor with levels 0 1

Examples

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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)