While Figure 4 shows the probability of emergence as a function of the number infected, the actual outcome is highly unpredictable even if the probability of an event is known as the average waiting time to an emergence shows (see equations 4 and 5). It can be generalized for the probability of emergence given x infectious hosts. For example, the probability of emergence given five infectious hosts in the gradual route (II) is p em (x~5)~0:567. It follows on average every 1:736 times this happens an emergence will happen. The standard deviation is +1:161, which leads to the conclusion that even if the probability is known, it is inherently unpredictable when this will actually lead to an emergence.