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What Sample Size Do I Need?

Six Sigma – iSixSigma Forums General Forums Tools & Templates What Sample Size Do I Need?

This topic contains 3 replies, has 3 voices, and was last updated by  Strayer 2 months, 2 weeks ago.

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  • #240759

    evan8818
    Participant

    I have a manufacturing company that will make 300,000 small metal parts a month that have a final process of being heat treated. The following are the parameters:

    Heat Treat: 79-85 HRA @ 0.025″ case depth.

    I am trying to figure out how many I need to sample to have a 99% confidence level with only 1% margin of error.

    Total pieces: 300,000

    750 buckets with 400 pieces per bucket.

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    #240761

    Katie Barry
    Keymaster

    @evan8818 This looks like a homework question. Please show how you approached/would approach this problem. If you got it wrong, where do you think you’re getting hung up? The more detail you show, the more likely you are to get a reply. The iSixSigma audience is helpful, but they are not here to do your work for you. They want to see that someone is putting forth a good-faith effort on their own first.

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    #240764

    evan8818
    Participant

    Defiantly not a homework question. I am currently doing 100% inspection in China but I am not confident it is up to the standards we are accustomed to here in the States. My company consists of me and two other people. We don’t have the time to do 100% inspection and that is why I am trying to find the best sample size for my population. With that population size how many random buckets should I choose if there are 750 buckets. My best estimate is 638 pieces but that seems too low. I am also implementing this so that I can get samples overnighted to me so that I can catch any issues before they get on a boat here as a double dip just to be sure.

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    #240770

    Strayer
    Participant

    If you don’t know the standard sample size calculation formulas, look them up on this site and elsewhere.  You can also find on-line sample size calculators.  Not trying to be snarky.  It’s just that you said your best “estimate” is 638 pieces and that doesn’t sound like you’ve done the math.  If you have and you still have questions about optimum sample size, describe your concerns and one of us may be able to give advice.

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