Flat log-rate marginalization gives the multinomial likelihood
= Flat log-rate marginalization gives the multinomial likelihood
{title2=$\int_0^\infty u^{n-1}e^{-Su}\,du=\Gamma(n)S^{-n}$}
For positive group totals, the <improper prior> $du/u$ on an independent Poisson baseline yields the <multinomial likelihood> kernel after integration. This prior is flat in $\log u$. A proper finite-variance log-rate prior generally introduces an additional coefficient-dependent factor.