HomeTechniques and TipsAdvanced Analyses in @RISKFix Distribution to Base Value When Not Stepping

8.1. Fix Distribution to Base Value When Not Stepping

Applies to: @RISK 5.x–7.x

In Advanced Sensitivity Analysis, on the Input Definition dialog, there is a check box, "Fix distribution to base value when not stepping". What does this mean?

You specify one output and one or more inputs in the Advanced Sensitivity Analysis dialog box. This check box matters only when you specify more than one input.

When multiple inputs are specified, Advanced Sensitivity Analysis begins with a set of simulations to determine the impact of the first input on the output. In each of those simulations, the first input has a particular value, which is one of the steps that you specified on the Input Definition screen. So for this first set of simulations as a group, we say that @RISK is stepping the first input.

Then Advanced Sensitivity Analysis continues with another set of simulations to determine the impact of the second input on the output. In this set, @RISK is stepping the second input. For each input, @RISK runs one simulation for each step you specified on the Input Definition screen for that input. After all the specified inputs have been stepped independently, @RISK prepares the sensitivity reports.

The question is, while @RISK is stepping a given input, what are all the other inputs doing? There are two possibilities:

The above applies only to inputs that are selected in the Advanced Sensitivity Analysis. During the simulations for that analysis, any @RISK inputs that are not selected as inputs in the Advanced Sensitivity Analysis dialog will vary randomly, just as they do during a regular simulation. You do have the option of locking any of them to prevent them from varying, but then you are doing an analysis without taking into account the uncertainties that you programmed into your model.

Last edited: 2015-07-14

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