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3.4. Setting the "Return Value" of a Distribution

Applies to: @RISK 5.x–7.x

For cells in my model that are probabilistic (directly or indirectly), how do I change the value that is displayed in the cell when a simulation is not running?

By default, when a simulation is not running you will see static values: the displayed values of @RISK distributions won't change during an Excel recalculation. The default static value for continuous distributions is the mean value (expected value). For discrete distributions, the default static value is not the true expected value but rather the value within the distribution that is closest to the expected value: for example, RiskBinomial(9,0.7) will display 6 rather than 6.3.

Outputs, and other values computed from the inputs, generally don't display their own mean or expected value but rather the value computed from the displayed values of inputs. Please see Static Value of Output Differs from Simulated Mean.

There are several ways you can change the displayed values of input distributions, and the resulting displayed values of outputs. None of these methods will affect a simulation in any way.

Which static values are displayed?

@RISK lets you choose to display the expected value, true expected value, mode, or a selected percentile for all distributions. You can make this choice in either of two places:

Simulation Settings, bottom half of the General tab: applies to all distributions in all open workbooks.
Utilities » Application Settings » Default Simulation Settings section » Standard Recalc: applies to all distributions in all open workbooks and to any new workbooks you create in the future when @RISK is running.

What's the difference between "expected value" and "true expected value"?

For continuous distributions, "expected value" and "true expected value" are the same, the mean of the distribution.

For discrete distributions, "true expected value" is the mean of the distribution, but "expected value" is the mean rounded to the nearest value that is a member of the distribution. For example, RiskBinomial(3, .44) has a mean = "true expected value" of 1.32, but an "expected value" of 1 because that is the nearest to the mean out of the distribution's possible values 0, 1, 2, 3. In other words, for the mean or expected value of discrete distributions, as defined in textbooks, you need to set @RISK to display the "true expected value".

You can also put a RiskStatic( ) function in an individual distribution to override the general settings, for that distribution only. Example:

=RiskNormal(100, 10, RiskStatic(25) )

Display random values instead of static values

You can suppress the static values and have @RISK generate new random values for each distribution when Excel does an automatic recalculation or when you press F9 to force a manual recalculation. To switch between random and static values for all open workbooks use either method:

"Rolling dice" icon (Random/Static Standard (F9) Recalculation).
Simulation Settings, bottom half of General tab, select Random Values or Static Values. (The "rolling dice" icon switches between these two.)

You can also change @RISK's default from static values to random values in the Application Settings dialog, as mentioned above.

Last edited: 2017-10-10

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