ABSTRACTS OF OTHER IIASA PUBLICATIONSS OF OTHER IIASA PUBLICATIONS Fedra, K., Mathematical Modelling a Management Tool for Aquatic Ecosystems? IIASA<lb>Research Report RR-81-2, March 1981.<lb>Reprinted from Helgolander Meeresuntersuchungen, Vol. 34, 1980, pp. 221-235.<lb>Mathematical modelling may serve as a rational and powerful tool in the manage-<lb>ment of complex ecosystems. However, ecosystem models are drastic simplications of the<lb>real world. As a rule they are based on a rather incomplete and scattered knowledge of<lb>the system in question. Furthermore, ecological systems and in particular marine systems<lb>are characterised by a high degree of complexity, spatial and functional heterogeneity,<lb>nonlinearity, complex behavioural features such as adaptation and self-organisation, and<lb>a considerable stochastic element. Nevertheless, if management is to be based on predic-<lb>tions from mathematical models and it has to be based on some kind of "model" in at<lb>least a broad sense we need an estimate of prediction accuracy in terms of the manage-<lb>ment variables and constraints. One possible approach to model uncertainty is a probabi-<lb>listic interpretation of model predictions, generated by use of Monte-Carlo techniques.<lb>Fuzzy data sets and ranges are used. The resulting model response allows the derivation of<lb>measures for model credibility. Probability distributions can be computed for certain sys-<lb>tem states under (un)certain input conditions, representing the effects of insufficient data<lb>and structural uncertainty on model-based predictions. Such analysis indicates that pre-<lb>diction uncertainty increases, not only with the uncertainty in the data, but also with<lb>increasing "distance" from the empirical conditions, and with time. Present ecosystem<lb>models can be a tool for qualitative discrimination between different management alter-<lb>natives, rather than a credible means for detailed quantitative predictions of system re-<lb>sponse to a wide range of input conditions. Clark, W.C., Witches, Floods, and Wonder Drugs: Historical Perspectives on Risk Manage-<lb>ment. IIASA Research Report RR-8 1-3, March 198 1.<lb>Reprinted from Richard C. Schwing and Walter A. Albers, Jr., editors, Societal Risk<lb>Assessment: How Safe is Safe Enough? New York: Plenum Press, 1980, pp. 287-<lb>314.<lb>Risk is a people problem, and people have been contending with it for a very long<lb>time indeed. I extract some lessons from this historical record and explore their implica-<lb>tions for current and future practice of risk management.<lb>Socially relevant risk is not uncertainty of outcome, or violence of event, or toxic-<lb>ity of substance, or anything of the sort. Rather, it is a perceived inability to cope satis-<lb>factorily with the world around us. Improving our ability to cope is essentially a manage-<lb>ment problem: a problem of identifying and carrying out the actions that will change the<lb>rules of the game so that the game becomes more to our liking.