  What has, by and large, become the standard classification of stochasticity goes back to a 1978 dissertation by Shaffer. The context of that dissertation provides a striking exemplar of the social determination of science. The United States National Forest Management Act of 1976 required the Forest Service to “provide for diversity of plant and animal communities based on the suitability and capability of the specific land  area.”[19]  In 1979 the planning regulations developed to implement this provision required the Forest Service to “maintain viable populations of existing native and desired non-native vertebrate species in the planning  area.”[20]  A viable population was defined as “one which has the estimated numbers and distribution of reproductive individuals to insure its continued existence in the planning area.” For large populations, falling within the domain of deterministic models, establishing viability is relatively trivial: all that must be ensured is that, on the average, a population is not declining in size. For small populations, even if it is increasing in size on the average, a chance fluctuation can result in extinction. Stochastic models are necessary to predict parameters such as the probability of extinction within a specified time period or the expected time to extinction.