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Line 35: * 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 + 1.645 × SD, for all project and task estimates.<ref>http://en.wikipedia.org/wiki/68-95-99.7_rule</ref> ~~<ref>http://en.wikipedia.org/wiki/68-95-99.7_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 20–30 tasks for this to be reasonable, and each of the estimates E for the individual tasks would have to be unbiased.

Three-point estimation: Difference between revisions