Tumor incidence in 71 groups of rate from Tarone (1982).
The matrix rat has 71 rows and 2 columns.
Each row relates to a different group of rats.
The first column (y) contains the number of rats with tumors.
The second column (n) contains the total number of rats.
Source
Table 5.1 of Gelman, A., Carlin, J. B., Stern, H. S. Dunson, D. B., Vehtari, A. and Rubin, D. B. (2013) Bayesian Data Analysis, Chapman & Hall / CRC. http://www.stat.columbia.edu/~gelman/book/data/rats.asc