There is an important choice to be made in assigning costs to the various actions that comprise an intervention strategy. A monetary valuation scheme is the most straightforward, but it may be difficult to construct such a scheme that adequately represents all aspects of the decision. One alternative would be a valuation in which each cost is chosen to represent a probability of mortality. In this way, the cost to be minimized would be the expected total loss of life for the epidemic under a given intervention strategy. By assuming that the removal rate can be expressed as r~mzv, where m is the rate of disease-induced mortality and v is the rate of natural recovery from the infected state, we can set c i~1 {e r ð Þ m r , so that the cost associated with maintaining a given number of infected individuals for a unit of time is the number of infected individuals that are expected to die in a unit of time. Similarly, situations exist where it is reasonable to assign a probability of mortality to the removal of susceptibles, as in the cases of smallpox vaccination or the culling of livestock.