Confidence & Reliability - Reference to a 90/95 Confidence & Reliability Level

J

johnnyB

I'm reviewing a sample size justification and am confused. The author of the plan makes reference to a 90/95 confidence and reliability level to determine sample size for attribute type data based on a binomial probability distribution. I always thought that only applied to variables data. I'm typically used to seeing LTPD or AQL levels to characterize attribute data. Is there is a correlation to the 90/95 C and R?

Thanks!

Miner

Forum Moderator
Staff member
Re: Confidence and Reliability

This is probably a reliability demonstration test plan. Units are tested to a specific point in time with no more than a specified number of failures to demonstrate a specified reliability (R) at a specified confidence (.95 or .90) level. This results in Pass/Fail (attribute) data.

This link to the Reliasoft website provides additional information. I am not affiliated with Reliasoft. I use Minitab, which can determine the appropriate sample size for a demonstration test. Unfortunately, they do not have this information available online.

Note: I am moving this thread to the Reliability forum.

T

teqp1

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Hi - sorry to hijack this thread, but my question seemed to fit this topic.

Can someone cite a reference for sample size for attribute data table? I have seen a table but can't locate it in any textbooks that I have. The table I am referring to is based on the Bayes Success Run Theorem for reliability and confidence, e.g. reliability of 95% and a confidence of 95% with 0 failures allowed in the samples would require 59 samples.

Thank you in advance for the help.

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Miner

Forum Moderator
Staff member
Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

[FONT=arial,helvetica,sans-serif][SIZE=-1]I could not locate the table to which you refer, but I did locate the formula that the table would have been based upon.
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[FONT=arial,helvetica,sans-serif][SIZE=-1][/SIZE][/FONT][FONT=arial,helvetica,sans-serif][SIZE=-1]

Bayes Success-Run Theorem (based on the binomial distribution).
R = (1-C) ^ (1/n) ;
R = Reliability (or probability of success) ,

C = confidence level ,

n = sample size. For "0" failures allowed on test
Given R=.95, C = .90 , solve for n
Ln(R)=(1/n)*Ln(1-C)
-.05129=(1/n)*(-2.30259)
n= 44.89 or 45.
[/SIZE][/FONT]

T

teqp1

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Miner,

Thank you for the information. Yes, that is the equation that I used and very certain that the table I am referring to is based on the same equation. I guess what I was looking for was a text that the table was in to use as a reference. Unfortunately, I don't have enough posts here to link a copy of the table I am referring to. I guess I need to post more!

Miner

Forum Moderator
Staff member
Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

The only text that I could locate was an abbreviated table on page 6 of this paper.

J

Juan Dude

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Can someone cite a reference for sample size for attribute data table? I have seen a table but can't locate it in any textbooks that I have. The table I am referring to is based on the Bayes Success Run Theorem for reliability and confidence, e.g. reliability of 95% and a confidence of 95% with 0 failures allowed in the samples would require 59 samples.
Is it this one (refer attached file)? Reference included.

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T

teqp1

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Juan Dude,

Thank you. That table is very similar to the copy I have, just formatting is different.
I had a question about the reference cited. Is the full title, Handbook of Reliability Engineering and Management? I can't locate the title cited under the authors. There is a Handbook of Reliability Engineering by a Hoang Pham with a 1st edition in 2003. But there is Handbook of Reliability Engineering and Management written by W.G. Ireson and C. F. Coombs.

Thank you for the clarification.

J

J

Juan Dude

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

The Reliability and Confidence Sample Size Calculator available here coincides with the table I posted above. If you calculate sample size required cor a C/R level of 95%/95% = 60 http://www.quality-one.com/products/inttools.php

It would be most interesting to replicate say in an excel sheet how the calculation is actually done, don't you think? I've been trying to do this for some time without any success

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