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https://open-psa.github.io/mef
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Log-Normal distribution Error Factor general formula/explanation #21

Closed rakhimov closed 7 years ago

rakhimov commented 7 years ago

The description of the Log-Normal distribution in the MEF is given specifically for one level only without providing a general formula for all levels. If the EF is defined only for 95% level, why does the MEF provides the "level" variable?

In fact, the EF parameter is very strange to me because I haven't seen this parameter in the definition/description of the log-normal distribution in statistics. This EF factor seems to be defined in PRA/PSA literature only. Honestly, this EF feels like another misnomer (e.g., fault tree, cut set) coming from the PRA. Let me explain why I have the suspicion.

  1. How on Earth, the 95% z of the standard normal distribution is 1.654 (Safety and Reliability: Proceedings of ESREL 2003, European Safety ..., Volume 2) (http://nrcoe.inl.gov/radscalc/Pages/AboutHTMLFiles/Distributions.htm) ? It must be 1.96.

  2. Why is the general formula/theoretical discussion absent?

This is my guess for the general formula:

EF_level = exp(z_level * sigma)

So the EF description in the MEF would be for 90% level.

Please destroy me!

rakhimov commented 7 years ago

Before anyone else destroys me, I now see that z_level must be one-sided; that how it ends up being 90% two-sided z.

rakhimov commented 7 years ago

Does EF for the level below 50% make any sense?