data(ducklings)p1, p2, p3
stand for pre-albumin, albumin, globulins respectively.
These were collected from 3-week old white Pekin ducklings.
Let $Y_1$ be proportional to the total milligrams of
pre-albumin in the blood serum of a duckling.
Similarly,
let $Y_2$ and $Y_3$ be directly proportional
to the same factor as $Y_1$ to the total milligrams
respectively of albumin and globulins in its blood serum.
The proportion of pre-albumin is given by
$Y_1/(Y_1 + Y_2 + Y_3)$,
and similarly for the others.dirichlet.