Fig. 1
From: Measuring the potential of individual airports for pandemic spread over the world airline network
Computing AEF for a single airport. In the sample network show here, an epidemic can spread from the seed airport “S” (red) in the following ways: (S→a,S→b), (S→b,S→a) as shown in panel (a), both resulting in onward transmission strength of 1+9=10; (S→b,S→c) shown in panel (b), resulting in onward transmission strength of 1+3+9=13; (S→b,S→d) panel (c), resulting in onward transmission strength of (6∗1)+3=9. Transmission strength along a given edge is shown by the number beside the edge. The transmission S→a occurs with probability 1/3, after which S→b is the only remaining option. Transmission S→b occurs with probability 2/3; implying pattern (S→b,S→a) has overall probability 2/3∗1/11=2/33, (S→b,S→c) has overall probability 2/3∗1/11=2/33, (S→b,S→d) has overall probability 2/3∗9/11=18/33. The distribution of FoI values scaled by their probability is thus: 10∗1/3,10∗2/33,13∗2/33,9∗18/33, and the AEF of airport S is 1.09, the entropy of this series after normalization