Some scenarios are presented purely as a written story - a narrative.
Others focus on tables or graphs of quantitative indicators - a set of numbers.
Most scenario exercises combine both.
In practice, the narrative and the numbers support and compliment each other
in important ways.
Because scenarios are stories, the
need for a narrative is usually clear. The role of the numbers
is sometimes less obvious. There are at least five roles that a numerical
analysis can play in a scenario exercise. It can:
- Force a clarification of terms and mechanisms.
- Expose contradictions in mental models.
- Provide a feel for the scope of possible outcomes within a narrative framework.
- Illustrate a particular scenario narrative.
- Make a study replicable, extensible and transferable.
In return, the narrative helps keep the quantitative analysis honest.
It is easy to get seduced by the seeming rigor and precision of a quantitative
computer model. However, for the sustainability problem, the uncertainties
are so great, and the state of knowledge is so limited, that computer models
are forced to exclude certain elements
in the real world. Sometimes the excluded elements are known to be
very important (for example, the informal economy
in developing countries). In such cases, a narrative
exercise can bring these elements
to the forefront.