Grouping Assumption Effects in Bridges
When two scenarios differ in whether an assumption is active at all, a bridge has two contributions to draw for it: the effect of taking it out of the start scenario, and the effect of putting it into the end scenario. Those two can step through the chart as separate bars, or be netted against each other into a single bar.
What it is
Group Assumption Effects is a toggle in a bridge’s settings. It decides which of the two you get:
| Toggle | What the bridge shows |
|---|---|
| Off | Two bars for an element whose contribution is both removed and added, with the removed one marked by a trailing *. A line-item’s variants each get their own bar. |
| On | One bar per element, netting its removed and added contributions against each other. A line-item’s variants are combined into their line-item’s bar. |
The toggle does not decide whether the bridge steps by assumption or by line-item. That comes from what you put on the axis in Configure Axes.
With the toggle off, the assumption Volume contributes two bars: Volume * for taking it out of the start scenario, and Volume for putting it into the end scenario.
With it on, the two net into a single bar:
When to use it
- The bridge has become long and hard to read because every assumption that switches on or off between the scenarios takes two bars.
- You want the chart to show what an assumption is worth on balance, rather than the removal and the addition side by side.
- A line-item has several variants and you want its total effect rather than one bar per variant.
Leave it off when the point of the chart is how much of an assumption’s effect comes from dropping it out of the start scenario and how much from adding it to the end scenario.
Configuration
- Select the bridge. The chart editor opens on the right.
- Go to Bridge Settings.
- Switch Group Assumption Effects on or off.
Good to know
- It groups variants too. When a bridge shows line-items with differing variants as deltas, rather than assumptions, the setting combines those variants into a single bar as well.
- It is a display setting. Grouping changes how the effects are drawn, never how they are calculated. See Assumption Effects.
- On a time bridge only the variant grouping applies. Both bridge types carry the toggle, but a time bridge compares a single scenario against its own baseline. Nothing is ever removed, so there is nothing to net and the
*bars never appear there. What the toggle still changes on a time bridge is whether a line-item’s variants are drawn as separate bars.
Related
- Assumption Effects: how the effect of an individual assumption is derived.
- Scenario Bridges: explain a difference between scenarios.
- Time Bridges: explain a difference between periods.
- Data Effects Display in Bridge: the equivalent grouping for the model’s own contribution.