On the Measurement of Information in the Field of Criminal Detection

Abstract

A method for measuring the value of information in those fields where the meaning of messages is important is discussed. At present there exists no accepted measure of information in such problem areas, the classical unit of bits flowing per second being unacceptable. It is shown that where two sets of phenomena are associated in some way with a given set of probabilities, e.g. a population and the crimes which are committed within it, the problem reduces to how much “choice” exists. This enables the concept of entropy to be used to advantage.

After developing a measure of the value of information in the general case, the paper applies the method to the investigation of a case of simple larceny. This case illustrates several interesting features. Perhaps the most important feature is that some pieces of information, although they are very important to the police, only change the level of uncertainty very slightly. In such cases the piece of information generally demands that the police perform an action which either may provide useful information or lead to further action. To overcome this problem a potential entropy change is defined which takes this factor into account.

It is hoped that the work may lead to a fuller understanding of how information flows in the police network. Thus it may be possible to see if the right information is getting into the police system, getting lost inside it or whether it is being used most efficiently.