1. How an outbreak affects pathway
likelihoods
An outbreak has occurred. Therefore:
• The pathogen must have entered along a
pathway; and
• The total likelihood of entry for all pathways
must equal 1. (The event must (did) occur.)

2. How an outbreak affects pathway
likelihoods—Example (1)
The analysis finds three pathways with these
likelihoods (per year):
a) By sea (p=10/10 000);
b) By land (p=20/10 000);
c) By air (p=1/10 000); and
d) No entry (p=9 969/10 000).

3. How an outbreak affects pathway
likelihoods—Example (2)
Given the outbreak, what are the likelihoods for
each pathway? (Hint: this is a Bayesian analysis)
a) Sea likelihood 10/10 000;
b) Land likelihood 20/10 000; and
c) Air likelihood 1/10 000.

4. How an outbreak affects pathway
likelihoods—Example (3)
Total likelihood is 31/10 000 before the
outbreak. Likelihood given an outbreak:
a) Sea (10/10 000)/(31/10 000);
b) Land (20/10 000)/(31/10 000); and
c) Air (1/10 000)/(31/ 10 000).

5. How an outbreak affects pathway
likelihoods—Example (4)
Total likelihood is 31/10 000 before the
outbreak. Likelihood given an outbreak:
a) Sea 10/31;
b) Land 20/31; and
c) Air 1/31.