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* ''b'' = the worst-case estimate
==Estimation==
Based on the assumption (possibly unwarranted) that a [[triangular distribution]] governs the data, several estimates are possible. These values are used to calculate an ''E'' value for the estimate and a [[standard deviation]] (SD) where:
: ''E'' = (''a'' + 4''m'' + ''b'') / 6
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''E'' is a [[weighted average]] which takes into account both the most optimistic and most pessimistic estimates provided. SD measures the variability or uncertainty in the estimate.
==Project management==
To produce a project estimate the project manager:
* Decomposes the project into a list of estimable tasks, i.e. a [[work breakdown structure]]
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* Confidence level in E value + 2 × SD is approximately 95%
* Confidence level in E value + 3 × SD is approximately 99.5%
* IS uses the 95% confidence level, i.e. E Value + 2 × SD, for all project and task estimates.
These confidence level estimates assume that the data from all of the tasks combine to be approximately normal (see [[Asymptotic distribution#Asymptotic normality|asymptotic normality]]). Typically, there would need to be 20–30 tasks for this to be reasonable, and each of the estimates E for the individual tasks would have to be unbiased.
== See also ==
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