# Sampling and confidence/precision

Six Sigma – iSixSigma Forums Old Forums General Sampling and confidence/precision

Viewing 9 posts - 1 through 9 (of 9 total)
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• #32796

Ropp
Participant

I was asked today to determine a sample size required for different confidence intervals (80, 90, and 95% respectively)
I have not found a way to accurately answer this question. Does anyone know of a way to either plug in a known population and sample size and get an estimate of CI, or plug in a population size and desired confidence level and get a sample size?
Thanks, and take it easy on me….I’m statistically challenged!

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#87969

Gabriel
Participant

Please be more descriptive. Confidence interval of “something” is the range where you expect “something” to be with a given confidence (like 80, 90, and 95% in your case). What is “something” in your case? (Examples: the rate of non-conforming parts in a batch, the average of a product characteristic, or its standard deviation, etc). What are you trying to do?

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#87970

faceman888
Participant

Gabriel is right.  You need to determine your acceptable margin of error as well as your level of confidence.  Here are some formulae that might help.
http://fire.r9.fws.gov/ifcc/monitor/RefGuide/ssequations.htm

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#87971

Ropp
Participant

I’m looking for defects present in an “event” (i.e., order entry errors)
what I’m being asked is what is the correct sampling rate if ‘m interested in 5% precision and a 90% or 80% confidence level, and I’ve only been able to find out 95% and 99% confidence sample sizes.
Can you help?

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#87980

Gabriel
Participant

https://www.isixsigma.com/forum/showmessage.asp?messageID=26744
https://www.isixsigma.com/forum/showmessage.asp?messageID=28849
You can also play in excel with the binomdist, poissondist and hypergomdist functions.
If you post a concrete example (real or not) you would like to solve, I will try to help you.

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#121384

Ron
Member

Dave,
In the Sampling and Margin of Error Page on this website there is a link to a calculator that will allow you to pick a confidence level and margin of error.  It asks for the population you are measuring and then will return a sample size.  This should allow you to build a quick matrix for others based on your population size.  No stats required.

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#164444

bum
Participant

Yes

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#164445

Bumface
Participant

Completely agree

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#164998

Moore
Member

Hi Ron you stated that In the Sampling and Margin of Error Page on this website there is a link to a calculator that will allow you to pick a confidence level and margin of error.
I have tried to find the page, can you direcr me?

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