LTPD (Lot Tolerance Percent Defective) Formula for Calculator

O

O2Arsenal

#1
Hello all,

I'm a newcomer to QA and the forum. I found a LTPD calculator in the website shown below and was wondering if any other knows what formula was used to establish this calculator. I tried doing some research online but wasn't successful in finding a formula for LTPD. Any help is appreciated and thanks in advance.

The website is statisticalsolutions.net ltpd_calc.php
 
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Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#3
<snip> I found a LTPD calculator in the website shown below and was wondering if any other knows what formula was used to establish this calculator. <snip>
If you want to know what formula they use on their web site I suggest you call the people who have the web site up. There is no one here who can tell you what formula they use on their web site. They give a phone number of: 608-345-4618
 
O

O2Arsenal

#4
If you want to know what formula they use on their web site I suggest you call the people who have the web site up. There is no one here who can tell you what formula they use on their web site. They give a phone number of: 608-345-4618
Thanks Harry and Marc for your response. Marc, I didn't have much luck with the number on their site. I am actually more interested in a formula to find %LTPD when the known variables are (#fails, #tested, and Confidence Level). It seems as though there might be a universal way or formula of solving %LTPD as another website at "maxim-ic" were getting the same results as the calculator in the website I mention in my first post.

Is this the case of solving for p in binomial distribution?

Pa = C(n,k)p^k* (1-p)^(n-k)
where n=#tested, k=#fails, Pa=confidence level
 

Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#5
I would be less than honest if I didn't say I wondered about your post because I think it would be quite unusual for someone here to know what formula another web site is using in their calculator.

I'm sure there is a formula, and maybe someone here can point you to it or post it here. I personally don't know what it is and have never used it so I can't help. All I ever used was Table X of MIL-STD-105E and Chart XV of ANSI Z1.4 for AQL and it's been a long time since I've worked with AQL. There is a ratio table of AQL to LTPD here: Approximate Ratio of LTPD/AQL.

Like Harry said, maybe someone will be able to help by giving you the formula as the forum starts picking up as the new week starts.
 
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A

Atul Khandekar

#6
Hello all,

I'm a newcomer to QA and the forum. I found a LTPD calculator in the website shown below and was wondering if any other knows what formula was used to establish this calculator. I tried doing some research online but wasn't successful in finding a formula for LTPD. Any help is appreciated and thanks in advance.

The website is statisticalsolutions.net ltpd_calc.php
Try doing a "View Source" on the web page...
 
C

CristianoP

#7
Is this the case of solving for p in binomial distribution?

Pa = C(n,k)p^k* (1-p)^(n-k)
where n=#tested, k=#fails, Pa=confidence level
There is no exact formula (we have p^k and (1-p)^(n-k)).

If you can write a PC program, the easiest and the fastest way is to use a binary search to find |Pa(p)-LTPD| < epsilon (it is the method that I use in my program). If you are interested in this method, let me know.

Cristiano
 
O

O2Arsenal

#8
There is no exact formula (we have p^k and (1-p)^(n-k)).

If you can write a PC program, the easiest and the fastest way is to use a binary search to find |Pa(p)-LTPD| < epsilon (it is the method that I use in my program). If you are interested in this method, let me know.

Cristiano
So are you saying %LTPD = (1-p)^(n-k)? If so, where does the confidence level come in.
 
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