ABSTRACT
The problem of expressing a probabilistic model may be reduced to the problem of determining a convenient way of expressing probabilities of events associated with random variables. This chapter describes the mathematical structure for describing a physical phenomenon in terms of a probability model. It is necessary to be careful to use a mathematical definition of probability which is consistent with the general physical understanding of probability. Various techniques may be useful in selecting appropriate numerical values for the probability function in a given physical situation. It is desirable to consider the probability of an event when it is known that the possible outcomes are restricted to some given subset of the original sample space. It is sometimes useful to consider conditional probabilities concerning one variable given knowledge about the other variables. The distribution of a random variable is called a life-testing model, and such models are considered in the area of reliability.
