The probability of disease.

This paper addresses the nature of the prior probabilities of diseases for probabilistic diagnostic reasoning. Because diseases differ in their chronicity, occurrence, reoccurrence, and likelihood of becoming part of the patient population, reasoning in terms of the frequency of disease episodes is necessary to capture the important distinctions. Even with these complexities, it is possible to formulate a reasonably accurate, computationally tractable, frequency estimation method for combinations of diseases. This method also suggests ways in which the needed numbers can be estimated from patient data.