© 1955 by Biometrika Trust
SOME THEOREMS AND SUFFICIENCY CONDITIONS FOR THE MAXIMUM-LIKELIHOOD ESTIMATOR OF AN UNKNOWN PARAMETER IN A SIMPLE MARKOV CHAIN
Australian National University Canberra, A.C.T.
The paper begins with proofs of the usual theorems for the optimum properties of the maximum-likelihood estimator of an unknown parameter
which defines the transition probabilities pij(
) of a simple ergodic Markov chain. By an ergodic chain is meant one for which, not only is the final chain stationary, but also all possible initial states remain permanently available; these conditions are sufficient to prove that the maximum-likelihood estimator is consistent, and asymptotically normally distributed.
The paper proceeds to establish the form of the transition probabilities pij(
) which admit a sufficient estimator of
. To do this, the form of the likelihood function admitting a sufficient estimator when the parent distribution is discrete is first derived: this is used to obtain the form of the probabilities Pij(
) for a multinomial distribution admitting a sufficient estimator of
. and the result is finally generalized for the transition probabilities pij(
) of the simple ergodic Markov chain.
The paper closes with an examination of possible forms for the matrix p of transition probabilities pij(
), and these are illustrated with simple examples for Markov chains with two and three states.