Lognormal distribution with alternative parameters






Format: LognormalAlt(Value1, Prob1, Value2, Prob2, Minimum)

 

Uses

This alternative parameterization of the Lognormal distribution is useful for modeling expert estimates of some continuous quantity with a long right tail, like time or cost to complete a task.

The LognormalAlt distribution appears in ModelRisk's standard Select Distribution palette. It also appears in the Expert selector window of ModelRisk when one selects two percentiles {(Value1, Prob1), (Value2, Prob2)} and a minimum.

ModelRisk has two other distributions that can be used with this alternative parametisation: the LogLogisticAlt and the WeibullAlt. It is a good idea to compare all three distributions together to see which gives the most realistic interpretation of the input parameters.

ModelRisk functions added to Microsoft Excel for the Alternative-Parameter Lognormal distribution

VoseLognormalAlt generates random values from this distribution for Monte Carlo simulation, or calculates a percentile if used with a U parameter.

VoseLognormalAltObject constructs a distribution object for this distribution.

VoseLognormalAltProb returns the probability density or cumulative distribution function for this distribution.

VoseLognormalAltProb10 returns the log10 of the probability density or cumulative distribution function.  

 

Alternative-Parameter Lognormal distribution equations

 

 

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