Configure Distribution

After a distribution has been selected it can be configured using the Configuration Panel on the left side of the Define Distribution window. All changes to the distribution function made through this panel will be reflected immediately in the Formula Bar. The Configuration Panel consists of three main sections:

Figure 1 - Distribution Parameters

  • Distribution - Primary settings for the distribution function (Figure 1, right); these include the type of distribution, standard or alternate parameters (where available), and those parameter values, e.g. mean (µ) and standard deviation (σ) for a Normal distribution.
  • Description - The distribution can be given a Name, a Category, and Units values.
  • Advanced - Set the Static Value to be displayed in the worksheet, configure the Random Number Seed settings, and set the Lock and Collect options.

Throughout the @RISK windows, the new More button ( ) indicates a menu or other window for selecting configuration options. For example, in the Define Distribution window, the More button will open the Select a Distribution window, where a new distribution can be selected, as well as the full menu for Parameter options.

Distribution Parameters

The mathematical definition of a distribution function is set in the Distribution section.

Function Field - This field lists the distribution type currently in use. Clicking the More button will open the Select Distribution window, where a new distribution type can be selected.

Parameters Field - All options for a distribution's parameters are set through this menu. For detailed information on the options available, please see Parameter Settings.

Parameter Values - These fields detail the specific values being used in the distribution; in addition to static values, parameter values can also use references to other Excel cells (including cells containing formulas or other @RISK distributions) enabling the creation of complex distributions. Several aspects of the available parameters will change depending on both the distribution being used and on the parameter options selected, including:

  • The number of required parameter values
  • The presence of truncation (numeric or percentile) and shift parameters
  • The format of the parameter values (integer values, percents, dates, etc.)

Description Properties

Figure 2 - Distribution Description

The Description fields (Figure 2, right) are used to attach labels to a distribution. Similar to parameter values, cell references can be used for these configurations. The options available are:

Name - The Name value will change the Graph title, as well as the Name value (the first column) for the input in the Model List. If no Name value is provided, @RISK will use the Automatic Names function.

Category - A category value can be assigned, which will group inputs together in the Model List.

Units - The Units value will change the label of the x-axis for any graph of the selected input.

When a Description property is set, note that @RISK functions are added to the main function; for example, when setting the Name property, the function RiskName, including the value entered, is added as an optional argument at the end of the main function.

Advanced Configurations

The final section of the Configuration Panel is the Advanced settings for the distribution. These settings control how the distribution results display within the Excel worksheet, the Random Number Seed used for the distribution, and whether or not the input is sampled when running simulations (see Sampling Settings under the Simulation Settings section for more information). The options available are:

Static Value - By default, a cell containing an @RISK function will display the value that corresponds to the Static Values setting in the Simulation Settings; see that section for more details on the setting and how it affects what is displayed in the Excel worksheet. However, this can be overridden for any input distribution. If another value should be displayed, that value can be set here. The Static Value setting in the Define Distribution window can be set to a number, a date, or even a cell reference.

Seed - The method used for random number generation during the execution of simulations; please note that this method can be set independently for each distribution. See Random Number Seed for more information.

This value should not be modified unless the full implications of the different Random Number Seed methods are understood; changing the Random Number Seed can have significant consequences to a simulation outcome!

Lock - Check this box to prevent sampling of the distribution when a simulation is run.

Collect - Check this box to includethe distribution when Inputs Marked with Collect is selected in Simulation Settings. See Sampling Settings for more information.