
306 ◾ Software Metrics
• If a subsequent x-ray test is positive (Figure 7.10b) our belief in both
TB (26%) and cancer (25%) are raised but bronchitis is still the most
likely (57%).
• However, if we now discover that the patient visited Asia (Figure
7.10d) we overturn our belief in bronchitis in favor of TB (63%).
Note that we can enter any number of observations anywhere in the BN
and update the marginal probabilities of all the unobserved variables. As
the above example demonstrates, this can yield some exceptionally pow-
erful analyses that are simply not possible using other types of reasoning
and classical statistical analysis methods ...