Supplementary Notes
Probabilistic framework for diagnostic process.
Definition 1: A symptom S is a Boolean random variable that takes its values in the set
{True, False}.
Definition 2. A symptom indicator IS is a continuous random variable that represents a
result of a measurement of a medical indicator that is relevant for determination of the
symptom presence. Generally it takes its values in a range [0...).
Definition 3. A certainty value of a symptom S for an indicator IS given its measured
value c is a mapping F: [0, )  [0, 1] such that F(S, c) = P(S | IS = c).
Definition 4: A disease D is a Boolean random variable that takes its values in the set
{True, False}.
Definition 5: A Diagnostic rule RD is a conjunction of one or more symptoms related to a
disease D. RD = S1S2…Sk .
Definition 6: The diagnostic rule, R, holds with probability p with respect to a set of
indicators {ISi} with values {ci} if the probability of all conjuncts to jointly hold equals p:
p  P( R  True) 

1i  k
F ( Si , ci ) 
 P(Si  True | I S i  ci )
1i  k
(We assume that all the evidences which belong to a diagnostic rule are independent).