Stress Analysis Simulations

The Stress Analysis command of the Simulation menu will run an analysis of the effects of stressing @RISK distributions. “Stressing” a distribution restricts samples drawn from the distribution to values between a specified pair of percentiles (e.g. only values that fall between the 30th and 60th percentiles). Alternatively, stressing can be done by specifying a new “stress” distribution that will be sampled instead of the original distribution in a model. With Stress Analysis a number of @RISK distributions can be selected simultaneously and simulations run while stressing these distributions jointly - either in one simulation, or separately in multiple simulations. By stressing the selected distributions, analysis of scenarios can be done without changing the overall model.

After completing a simulation, Stress Analysis provides a collection of reports and graphs useful for analyzing the effects of stressing certain distributions on the selected model output.

The Stress Analysis window (Figure 1, right) contains the following configurations:

• Cell To Monitor - The single output cell to monitor as the specified input distributions are stressed.

• Use the Model button ( ) to open a list of outputs in the current model and quickly select one!

• Inputs - The list of inputs that will be stressed during simulation. See below for information on configuring inputs.

• To add an input to be stressed, click the Add button.

  To edit or delete an input, select it in the list and click the Edit or Delete button.

Configuring Stressed Inputs

When the Add or Edit buttons (see above) are clicked, the Input Definition window (Figure 2, right) will open, allowing a new input to be defined or an existing input to be modified. The Input Definition window contains the following configurations:

• Type - Currently, only @RISK distributions can be selected as inputs for Stress Analysis, so the only option is 'Distributions'.
• Reference - The cell reference for the distribution to stress. Multiple inputs can be selected simultaneously if the variation method to be used for those inputs is identical.

• Use the Model button ( ) to open a list of inputs in the current model and quickly select one!

• Name - For Stress Analysis, the Name field will be automatically populated with the distribution's name. The Name value is used in Stress Analysis reports.
• Method - Select the method of variation for the input distribution during the analysis. The options are:
• • Stress Low Values - Specifies a low range from which to sample, bounded at the low end by the distribution minimum. The default is 5% as the upper percentile allowed; that is, only values between 0% and the 5th percentile of the distribution are allowed.
  • Stress High Values - Specifies a high range from which to sample, bounded at the high end by the distribution maximum. The default is 95% as the lower percentile allowed; that is, only values above the 95th percentile are allowed.
  • Stress Custom Range of Values - Specify any percentile range from which to sample values.
  • Substitute Function or Distribution - Enter an alternate function or formula - either an @RISK distribution function or any valid Excel formula - that will be substituted for the selected distribution during a Stress Analysis.
• Lower Percentile - Set the specific percentile to be used as the lower limit; any percentile value can be set.
• Upper Percentile - Set the specific percentile to be used as the upper limit; any percentile value can be set.
• Function (not pictured above) - The @RISK distribution function or Excel formula to be used during Stress Analysis.

• Use the button to the right of the Distribution/Formula box to use Excel’s Function Wizard to enter an alternate distribution.