the estimate of b is (Bennett and Franklin, 1954, p. 224)
=S=(X_{i} - [=X])(Y_{i} - [=Y])
[^b] = -------------------------------
=S=(X_{i} - X)^{2}
and of a is
â = [=Y] - [^b][=X]
where X_{i} = ln A for each group with known population and Y_{i} = P
for each known group.