Applies to: @RISK 5.x and Up

RiskPert Distribution

@RISK’s RiskPert distribution has three parameters: min, mode, and max.

Some references mention a four-parameter PERT with a shape λ, but RiskPert implicitly uses λ = 4.

You can mimic a four-parameter PERT using RiskBetaSubj:

[
\mu = \frac{\text{min} + \text{max} + \lambda \cdot \text{mode}}{\lambda + 2}
]

Then define:

RiskBetaSubj(min, mode, μ, max)

Example with min, mode, max, λ in B1:B4:

=B1 + B3 + B4*B2)/(B4 + 2)  → put in B5
=RiskBetaSubj(B1, B2, B5, B3)

This effectively gives a PERT with a custom shape parameter λ.

 

Attachments:
KB1474 Modified Pert with Shape.xlsx