Simultaneous Estimation of Multinomial Cell Probabilities

Abstract

A new estimator, p*, of the multinomial parameter vector is proposed, and it is shown to be a better choice in most situations than the usual estimator, (the vector of observed proportions). The risk functions (expected squared-error loss) of these two estimators are examined in three ways using: (a) exact calculations, (b) standard asymptotic theory, and (c) a novel asymptotic framework in which the number of cells is large and the number of observations per cell is moderate. The general superiority of p* over in large sparse multinomials is thus revealed. The novel asymptotic framework may also provide insight in other multinomial problems.