The black-footed ferret is an endangered species; it belongs to the weasel family. A ferret-breeding program has been established by various zoos throughout the United States to study the factors that affect breeding success in captive ferrets. The sample consists of 664 females, 375 males, and 1700 M-F pairings. In one season, a given female may occur in up to four pairings; a male may occur in up to  eight pairings. A given pair of ferrets may occur in two or more pairings in the same season or in different seasons.

The following variables are recorded at birth for each ferret:

\[
\text { ferret_id, sex, birth_year, zoo_id; }
\]

There are six participating zoos, and zoo_id is the zoo of birth. The following variables are recorded for each of the \(1700 \mathrm{M}\)-F pairings:

\[
\text { male_id, female_id, zoo_id, year, kinship, whelped; }
\]

The kinship coefficient is a standard measure of genetic relatedness of the breeding pair. The unit of observation is a male-female pairing, and the response is whelping success, which is binary.

In most cases, the ferrets spend their life at the zoo of birth, so zoo_id is the zoo of birth of both ferrets. However, inter-zoo transfers are possible, in which case the breeding zoo might be different from the zoo of birth for one or other ferret. The goal is to identify factor combinations that promote breeding success.

Discuss the role of each variable in this study.

Ferrets live about 4-6 years in captivity, so ferret age may be important for breeding success. Given that there are two ferrets in each pair, discuss how you would compute the age of each ferret, and how you would incorporate age effects into any model. Available options include linearly, symmetrically, additively, and so on.

male_id is an equivalence relation on pairings, as is female_id. What bearing does this have on modelling?