Decision

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Decision variable is a special kind of variable: it contains information about possible policy options. Structurally it is similar to other variables, but the decisions have a special role in causal diagrams, as that is usually the starting point of the diagram. The descriptions of decision variables and scenarios are performed according to the variable structure and using the standard functionalities of the toolbox.

A scenario is a particular value from the distribution of plausible options (values) of a decision variable. It can also be a set of particular values from several decision variables. For policy assessments, often several scenarios are defined and then compared to each other, e.g. if the impacts of a certain policy (measure) is assessed. A good analysis practice is that a business-as-usual scenario (BAU) is always included in an assessment. BAU is a scenario where active measures are not taken in addition to those that have already been decided. A particular set of scenarios can be saved and used in several risk assessments. A scenario therefore can be a part of an assessment but is not an assessment itself.

The result of a decision variable contains the range of the plausible options. This range should be generalizable to all assessments. For a particular assessment, the assessor may choose values from within (but not outside) the range of plausible values has he pleases, as long as the business-as-usual option is included. The business-as-usual option is distinguished from other options by the shape of the result distribution: the business-as-usual option should have a clear peak, while other options should show a more or less uniform distribution (or some other distribution reflecting the probability of each decision outcome).D↷ A particular plausible option, decided by the risk assessor for a particular risk assessment, is called a scenario. Therefore, a scenario is a property of a risk assessment, not a property of a variable.<section end=glossary />