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Sampling and confidence/precision

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

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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

    Thanks for your question.
    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

    Faceman provided a good link. These forum threads may also help.

    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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