HomeTechniques and Tips@RISK Simulation: Graphical ResultsExcluding an Input from the Sensitivity Tornado

7.11. Excluding an Input from the Sensitivity Tornado

Applies to: @RISK 5.x–7.x

How can I tell @RISK not to include one or more inputs in tornado charts and other sensitivity results including RiskSensitivity( ) and RiskSensitivityStatChange( )?

You might want to do this if you have two inputs that are very highly correlated. This creates multicollinearity, which adds a redundant bar to the Change in Output Statistic tornado and distorts the Regression Coefficients tornado.

The key is the RiskMakeInput( ) function. @RISK excludes all the predecessors of a RiskMakeInput( ) from sensitivity analysis, whether or not that RiskMakeInput( ) is a precedent of any output. Thus, all you have to do to exclude P11 and J15 from sensitivity measurements is to put them in a simple RiskMakeInput in a previously empty cell:

=RiskMakeInput(P11+J15)

A nice feature of this approach is that you don't have to make any changes to the formulas in your actual model. Also, if you add or remove rows or move cells, Excel will automatically update the cell references, just as with any other formula. However, the RiskMakeInput( ) itself will now appear as an input in sensitivity functions and graphs. To prevent that from happening, multiply the included expression by 0, so that every iteration value is the same:

=RiskMakeInput(0*(P11+J15))

Finally, you might want to add a short comment explaining the function of this RiskMakeInput( ), so that years from now you or someone else won't be tempted to delete it when updating the workbook. You can do this in a RiskName function:

=RiskMakeInput(0*(P11+J15),RiskName("Exclude cells from tornado"))

If you have multiple RiskMakeInput functions, you can use the same comment in all of them. The duplicates won't be a problem for @RISK as long as you don't try to use those names in @RISK statistic functions like RiskMean( ) or RiskPercentile( ), which you have no reason to do.

To make the change effective, you'll need to run a new simulation. Please see the attached example.

RiskMakeInput( ) will work as described here, whether Smart Sensitivity Analysis is enabled or disabled in Simulation Settings.

I don't want to recalculate results; I just want to suppress one or more bars of the tornado.

Right-click each bar you want to suppress, and click Hide Bar. If you want to bring the hidden bars back, right-click the graph and select Restore Hidden Bars.

See also: Combining Inputs in a Sensitivity Tornado.

Last edited: 2015-10-16

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