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How to use the Custom Distribution in Crystal Ball– The General Distribution (Tip #3 of 5)
The following Risk Analysis Tip is provided by Dr. H. Groenendaal (Huybert@risk-modeling.com) at Vose Consulting, and has been drawn from material in ModelAssist® for Crystal Ball®, the comprehensive risk analysis training, reference and template software. ModelAssist users can consult the ModelAssist-references (in the form of Mxxx) for additional information. To read more about ModelAssist and get a free download of the demo version, click here or go to http://www.decisioneering.com/modelassist/index.html.
Introduction
The Custom Distribution in Crystal Ball is one of the most versatile, but also one of the most difficult distributions to correctly use within Crystal Ball. In fact, using the Custom Distribution, a Crystal Ball user can construct five different kinds of distributions (see Table below).
Each of these five distributions have different uses and applications. The way that the Custom distribution “knows” which of the above five to make for you totally depends on the format of your input data ("date entry rules").
The goal of this (and the last tip and the next three) Risk Analysis tip(s) is to make you aware of the five different distributions that you can construct using the Custom Distribution and their various uses. The five Tips will also provide detailed instructions on how to format your data to construct the five different distributions with the Custom Distribution.
Important Note – Dynamic Referencing
When you use the Custom Distribution, we highly recommend that you use data from your spreadsheet and use “dynamic referencing” with the Custom Distribution because this allow the user to change data in his/her spreadsheet, which will result in appropriate changes in the distributions. You can read more about that in the Previous Risk Analysis Tip (Tip 1 of 5) .
1. The General distribution.
The General distribution is often used for:
- modeling expert opinion,
- modeling distribution not available with Crystal Ball and
- modeling posterior distributions in Bayesian inference.
For more information about the applications of the General distributions, see ModelAssist topic M0203.
General distribution is a continuous distribution and in Crystal Ball also called "sloping continuous ranges" distribution. Crystal Ball 7.0 requires a 5-column format as is shown in the figure below.
The five columns contain the following values:
- The first column has the minimum value of a range (but is left blank if the minimum is equal to the last range's maximum, see G11:G17)
- The second column has the maximum value of a range
- The third column has the relative probability height of the minimum (but is left blank if the height of the minimum is equal to the last range's maximum's height, see I11:I17)
- The fourth column is the relative probability height of the maximum
- The fifth column is left blank but is necessary to indicate that this is a General Distribution.
The figure below show the result of the five steps above.
What’s next?
If you like to know more about the Custom Distribution (or about Quantitative Risk Analysis in general), download the free demo of ModelAssist for Crystal Ball. This comprehensive risk analysis reference and training tool will help you perform accurate risk analyses with the Crystal Ball software.
ModelAssist
The material within this ‘Risk Analysis Tip’ comes from one of the over 500 risk analysis topics available in ModelAssist for Crystal Ball, which gives a more detailed explanation of the above methods and any risk analysis techniques involved.
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