Scenario Background

How Many Scenarios?

How many scenarios are needed for a scenario exercise? The consensus seems to be settling on either three or four scenarios. Here are the arguments.

One scenario

In nearly every case, a single scenario is insufficient. A single scenario can stimulate thought, but by itself it cannot support an exploration of different options.

Two scenarios

So, at least two scenarios are needed. This may be useful if it delimits a range. However, since the brackets of the range are normally extreme, they do not indicate how moderate action might achieve goals.

Three scenarios

This brings us to three scenarios at a minimum. The problem with three scenarios is that the middle scenario is likely to be interpreted as a “most likely” or “preferred” scenario by the users of the scenario. However, it is rarely the case that the central scenario is thought to be most likely or preferred by its designers.

Four scenarios

When possible, four scenarios is perhaps the best choice. In this case there is no middle scenario and the users of the scenarios are more likely to look at the full range of scenarios, rather than focusing on just one, as they are likely to do in a three-scenario study. However, the more scenarios there are, the more resources required to complete them. Also, more attention is required from the audience, and it is important to show respect for your audience by not overwhelming them with a large volume of work.

More than four scenarios

The need to not overwhelm the audience rules out the possibility of using more than four scenarios. It has been tried, and is generally thought to be counter-productive. The one situation where this might not be the case is when a small number of driving forces are combined in different combinations to produce a large number of resulting scenarios. In this case, the results can sometimes be presented in a grid or other arrangement that allows the patterns to be grasped quickly.

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