Polynomial Birth-Death Distribution Approximation in the Wasserstein Distance

The polynomial birth-death distribution (abbreviated, PBD) on I={0,1,2,aEuro broken vertical bar} or I={0,1,2,aEuro broken vertical bar,m} for some finite m introduced in Brown and Xia (Ann. Probab. 29:1373-1403, 2001) is the equilibrium distribution of the birth-death process with birth rates {alpha (i) } and death rates {beta (i) }, where alpha (i) a parts per thousand yen0 and beta (i) a parts per thousand yen0 are polynomial functions. The family includes Poisson, negative binomial, binomial, and hypergeometric distributions. In this paper, we give probabilistic proofs of various Stein's factors for the PBD approximation with alpha (i) =a and beta (i) =i+bi(i-1) in terms of the Wasserstein distance. The paper complements the work of Brown and Xia (Ann. Probab. 29:1373-1403, 2001) and generalizes the work of Barbour and Xia (Bernoulli 12:943-954, 2006) where Poisson approximation (b=0) in the Wasserstein distance is investigated. As an application, we establish an upper bound for the Wasserstein distance between the PBD and Poisson binomial distribution and show that the PBD approximation to the Poisson binomial distribution is much more precise than the approximation by the Poisson or shifted Poisson distributions.