Alternative representations of a Bayesian network for a search of a database of size n > 2. Bayesian network shown in Figure 5 with expanded representation of nodes along with an additional node H1with states H1(‘the suspect is the source of the crime stain’) and (‘some person other than the suspect is the source of the crime stain (either someone else in the database or an individual outside the database)’). Both figures show a situation in which the size n of the database equals 100 and that of the suspect population, N, equals 1,000. The rarity of the corresponding characteristic is set to 0.01. (i) Illustration of the evaluation of the numerator of the likelihood ratio for the item of information X2&…&X
(that is, none of the n−1 individuals in the database other than the suspect corresponds to the crime stain): H1is set to ‘true’, and the value of the numerator is shown in the node X2&…&X
. (ii) An evaluation of the denominator of the likelihood ratio (that is, is set to ‘true’). Probabilities are shown in percentages.