Applies to:
@RISK 6.x and up

 

Understanding @RISK RiskGamma Parameters

• @RISK RiskGamma uses two parameters:

  • α (alpha) = shape

  • β (beta) = scale

• Other sources may use different conventions:

  Source	Parameters	Relation to @RISK
  Wikipedia	shape (k), scale θ	α = k, β = θ
  Wikipedia	shape (k), rate β	α = k, β = 1/β
  Wikipedia	shape k, mean μ	α = k, β = μ/k

• Mean:

  • @RISK: ( \text{mean} = \alpha \cdot \beta ) (matches αθ in Wikipedia scale form)

Entering Parameters from an External Source

• Shape & Scale: α = shape, β = scale

• Shape & Rate: α = shape, β = 1 / rate

• Shape & Mean: α = shape, β = mean / shape

• Always ensure you convert any "rate" parameter to scale by taking its reciprocal.