Ability of retinyl acetate to prevent mammary cancer in rats
A total of 76 female rats were injected with a carcinogen for mammary cancer. Then, all animals were given retinyl acetate (retinoid) to prevent mammary cancer for 60 days. After this phase, the 48 animals that remained tumor-free were randomly assigned to continue the retinoid prophylaxis or control. Rats were then palpated for tumors twice weekly, and observations ended 182 days after the initial carcinogen injections began. The main objective of analysis was to assess the difference in the development of tumors between the treated and control groups. See Morel and Nagaraj (2012, page 63).
data(mammary)
A data frame with 48 rows and 2 variables:
a factor giving the group to which the rat was assigned: "retinoid" or "control".
a numeric vector giving the number of tumors identified on the rat.
Lawless J.F. (1987) Regression Methods for Poisson Process Data. Journal of the American Statistical Association, 82, 808-815.
Morel J.G. and Nagaraj N.K. (2012) Overdispersion Models in SAS. SAS Institute Inc., Cary, North Carolina, USA.
boxplot(tumors ~ group, data=mammary, outline=FALSE, xlab="Group",
ylab="Number of tumors", col=c("yellow","blue"))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.