PARAMETER-ESTIMATION FOR PROBABILISTIC DOCUMENT-RETRIEVAL MODELS

Probability distributions that may be used to describe the distribution of features include binary and Poisson distributions. Techniques for estimating the parameters of distributions are suggested. A proposal has been tested that parameters of distributions describing the distribution of features in nonrelevant documents be estimated from the parameters of the corresponding distributions of the entire database; the confidence parameter of such an estimate resulting in the highest average precision is given. Tests of several methods for estimating the parameters of distributions describing the distribution of features in relevant documents suggest that small values of the confidence parameter be used in initial estimates of parameters for relevant documents.