Three-point estimation: Difference between revisions

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* Confidence level in E value +/- 2 × SD is approximately 95%
* Confidence level in E value +/- 3 × SD is approximately 99.7%
* Information Systems typically use the 95% confidence level, i.e. E Value + 2&nbsp;&times;&nbsp;SD, for all project and task estimates.<ref>http://en.wikipedia.org/wiki/[[68-95-99.7_rule7 rule]]</ref>
 
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&ndash;30 tasks for this to be reasonable, and each of the estimates E for the individual tasks would have to be unbiased.