ON THE STRUCTURE OF BLACKWELLS EQUIVALENCE CLASSES OF INFORMATION-SYSTEMS

In this paper we follow Marschak in exploring the structure of Blackwe ll's equivalence classes of information systems. The main result is a full characterization theorem showing that two information systems are equally informative iff for every given a priori probability vector b oth generate identical sets of posterior probability vectors and some technical condition is met. We then show that for some special subsets of information systems, two information systems are equally informati ve iff one is a permutation of the other.