LogLogistic distribution with alternative parameters





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

 

Uses

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

ModelRisk has two other similar distributions that can be used with this alternative parametisation: the LognormalAlt 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 LogLogistic distribution

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

VoseLogLogisticAltObject constructs a distribution object for this distribution.

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

VoseLogLogisticAltProb10 returns the log10 of the probability density or cumulative distribution function.

Alternative-Parameter LogLogistic distribution equations

 

 

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