Creating scenarios

What is a scenario?

Scenarios let you set up different... scenarios. This is useful when comparing different discrete options. For example, you might be trying to decide whether to hire 5 people or 10 people this year.

A scenario is a variant of your model in which some variables have different values or formulas. The structure of the model — the variables, groups, and sections — doesn't change across scenarios.

You can visualise multiple scenarios together in charts and tables, to easily compare them. See comparing scenarios in charts/tables.

You can't perform calculations across scenarios. For example, you can't sum the values of a variable under different scenarios.

How do scenarios interact with the base model? (aka "default scenario")

A scenario is a live variant of your model in which some variables (or cells of a variable) have different values or formulas. The structure of the model — the variables, groups, and sections — doesn't change across scenarios.

• If you change (override) the formula/value of a cell, that cell will no longer be linked to the default scenario (but the rest of the variable will).
• If you change (override) the entire variable's formula, then the entire variable will no longer be linked to the default scenario.
• Any variables/cells you do not change/override will still be linked to the default scenario (so any formula/value updates in the base model will flow through).
• If you want to remove the override in the scenario, hit "Reset row" or "Reset override". This will revert the formula to match the default scenario, and reinstate the link (so that any future updates to the base model will flow through).
• Variables/cells that have been changed in a scenario will have a pink background.

Let's consider an example to illustrate how scenarios work:

1. You have a variable, Growth Rate, with a value of 10% in the default scenario.
2. You create a new scenario, S1.
3. In the default scenario, you change Growth Rate to 15%. This change will be applied to both the default scenario and S1, so Growth Rate will be 15% in both scenarios.
4. Next, you navigate to scenario S1 and change Growth Rate to 20%. This action "unlinks" Growth Rate in S1 from the default scenario. The variable will be highlighted in purple within the scenario to indicate this dissociation.
5. Now, you return to the default scenario and change Growth Rate back to 10%. Since the variable has been overidden in S1, this modification will not affect Growth Rate in S1 anymore.

Creating scenarios

There are two ways to create a scenario:

1. Right-click on a variable and click New Scenario
2. Click on Scenarios in the toolbar, and then click Add new scenario.

Note: if you have a set of linked models - the Scenario will automatically apply across all models. If you subsequently create a new linked model they will be automatically pulled across.

Scenario mode

Selecting a scenario under Scenarios in the toolbar, will take you into Scenario mode. In this mode, you'll be able to change the value of any variable/cell, and this change will only be applied in the active scenario.

You also have the following actions by clicking the Scenarios button (as per screenshot below):

• Rename the scenario by double-clicking the name
• Inspect the scenario by hitting :question:
• Clone the scenario
• Delete the scenario
• Override the default scenario with the selected scenario
  • If other scenarios exist after overriding the default model with another, all unchanged values for variables in the other scenarios will all revert to the values of the new, default model.
  • In other words, if you have a base model and two additional scenarios: Scenario A and Scenario B, and the base model is overridden by Scenario A to be the default model, then all of the variables in Scenario B that were unchanged from the original, default scenario, those variables will now take on the values of the new, default scenario)