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**Variable Selection in Tornado Graphs**

**Applies to:**

@RISK for Excel 4.x–7.x

@RISK for Project 4.x

How does @RISK decide which variables to include when I create a tornado diagram with regression coefficients?

To choose inputs to include in the tornado diagram, @RISK uses a stepwise multiple linear regression procedure. By default, each variable is accepted or rejected for the regression procedure at the critical value of 3.29 in the F distribution. For a technical reference, please see "The Stepwise Regression Procedure" in Draper and Smith, Applied Regression Analysis (Wiley, 1966).

An example is attached. For comparison, the Sensitivity sheet shows regression coefficients computed by @RISK, and the Regression sheet shows regression coefficients computed by StatTools. The order of variables is different between the two, because the two products read and store data in different ways. However, both sheets show the same coefficients, because they're doing the same type of analysis.

To set the maximum number of tornado bars in @RISK 6.x/7.x, please see Tornado Graph — How to Set Defaults. In @RISK 5.x, use Utilities » Application Settings » Simulation Graph Defaults.

**Additional keywords:** Sensitivity analysis

Last edited: 2016-10-20

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