format
A 'CBData' object, that is a data frame with the following variables
ll{
Trt factor giving treatment group
ClusterSize the size of the litter
NResp the number of affected fetuses
Freq the number of litters with the given ClusterSize/NResp combination
}source
Krewski, D., Zhu, Y. & Fung, K. (1995). Statistical analysis of overdispersed multinomial data from
developmental toxicity studies. In Statistics in Toxicology, Ed. B. Morgan, pp. 151--179. New York: Oxford University Press.