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

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  #1  
Old 28th April 2009, 05:58 PM
johnnyB

 
 
Posts: 1
Please Help! Confidence & Reliability - Reference to a 90/95 Confidence & Reliability Level

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!

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  #2  
Old 28th April 2009, 06:32 PM
Miner's Avatar
Miner

 
 
Posts: 3,542
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.
Thanks to Miner for your informative Post and/or Attachment!
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  #3  
Old 5th May 2009, 06:41 PM
teqp1

 
 
Posts: 7
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.

Last edited by teqp1; 5th May 2009 at 06:43 PM. Reason: typo
  #4  
Old 5th May 2009, 07:26 PM
Miner's Avatar
Miner

 
 
Posts: 3,542
Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

I could not locate the table to which you refer, but I did locate the formula that the table would have been based upon.



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.
Thanks to Miner for your informative Post and/or Attachment!
  #5  
Old 6th May 2009, 12:54 PM
teqp1

 
 
Posts: 7
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!
  #6  
Old 6th May 2009, 07:06 PM
Miner's Avatar
Miner

 
 
Posts: 3,542
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.
  #7  
Old 6th May 2009, 08:32 PM
Juan Dude's Avatar
Juan Dude

 
 
Posts: 250
Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Quote:
In Reply to Parent Post by teqp1 View Post

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.
Attached Thumbnails
Sample size for Attributes.JPG  

Last edited by Juan Dude; 7th May 2009 at 12:06 PM.
Thank You to Juan Dude for your informative Post and/or Attachment!
  #8  
Old 7th May 2009, 10:27 AM
teqp1

 
 
Posts: 7
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.
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