ABSTRACT
Uncertainty is a term that embraces a variety of concepts (Morgan and Henrion 1990). It may arise because of vaguely stated policy goals, e.g., continued use of pesticides should not affect the sustainability of raptor populations. Uncertainty may arise because of differences in our preferences, e.g., what exactly is “acceptable” risk. It may refer to lack of knowledge about model structure, e.g., how should pesticide intake via preening be estimated, or lack of knowledge about a quantity like Henry’s law constant for pesticide X. Uncertainty can sometimes be combined with the concept of variability, e.g., food intake rates among individuals in a flock of birds. Uncertainty also exists at different scales (e.g., spatially, temporally, levels of biological organization, etc.). These and other types of uncertainty can generate considerable confusion and often rancorous debate. As a result, there have been several attempts to classify types or sources of uncertainty (Finkel 1990; McNeill and Freiberger 1993; Hoffman and Hammonds 1994; Rowe 1994; Smith and Shugart 1994). Morgan and Henrion (1990) argue that it is crucial to distinguish between different types and sources of uncertainty, at least partly because they need to be treated in different ways in risk analyses.
