On the non-existence of ml estimates in the negative multinomial distributions derived from nonstationary poisson processes
Jugal K. Ghorai, Sanjoy Ghose · Communication in Statistics- Theory and Methods · 1996
Lenk, Rao and Tibrewala (1993) have introduced a Negative Multinomial Distribution derived from a nonstationary Poisson process with intensity function , which incorporates marketing mix variables. It is shown that under certain conditions, the maximum likelihood estimates of the parameters of the proposed model do not exist.