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Download a pdf copy of this help file here |
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Download a pdf copy of this help file here |
Format: VoseWeibullAlt(value1, probability1, value2, probability2 ,minimum,
U)
This alternative parameterization of the Weibull distribution is useful for modeling expert estimates of some continuous quantity with a long right tail, like time or cost to complete a task. It is often more easy for experts to talk about percentiles, like “there is a 5% chance the cost will be less than $100k”. This parameterization allows one to define a distribution using two percentiles and a minimum.
The WeibullAlt distribution appears in the standard Select Distribution palette. It also appears in the Expert selector window when one selects two percentiles {(P1, X1), (P2, X2)} and a minimum.
ModelRisk has two other distributions that can be used with this alternative parametisation: the LognormalAlt and the LogLogisticAlt. It is a good idea to compare all three distributions together to see which gives the most realistic interpretation of the input parameters.
VoseWeibullAlt generates values from this distribution or calculates a percentile.
VoseWeibullAltObject constructs a distribution object for this distribution. Professional and Industrial editions only.
VoseWeibullAltProb returns the probability density or cumulative distribution function for this distribution. Professional and Industrial editions only.
VoseWeibullAltProb10 returns the log10 of the probability density or cumulative distribution function. Professional and Industrial editions only.