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Thread: No Standard Deviation

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    No Standard Deviation




    Hello statistical geniuses,

    I have 450 items and I want to test a sample and be sure with 95% confidence that if all of my tested items are functioning properly, that 95% of my total population will be functioning properly. Is this possible? Thanks a lot for the help.

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    Re: No Standard Deviation

    Why do you want to use a sample when you have the population? Normally you sample because you can't obtain the whole population.

    I don't understand what you mean by "functioning properly" or what this has to do with standard deviation.
    "Very few theories have been abandoned because they were found to be invalid on the basis of empirical evidence...." Spanos, 1995

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    Re: No Standard Deviation

    Quote Originally Posted by noetsi View Post
    Why do you want to use a sample when you have the population? Normally you sample because you can't obtain the whole population.
    Just because you can make a list of the items in the population doesn't mean you have the measurements on those observations.

    I don't understand what you mean by "functioning properly" or what this has to do with standard deviation.
    My guess is that "functioning properly" is just what it sounds like - does the item do what it is supposed to do. It's a yes/no response. My guess is that the OP is somewhat familiar with sample size calculations for continuous data but doesn't have experience dealing with binary data and wants input on how to do a sample size calculation for this type of scenario.
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    Re: No Standard Deviation

    Hi, sorry for the confusion. I have the entire population, but given the amount of time and work involved, I don't want to have to test all 450 items. I was just curious if there was a way to test a sample, say 50, and if all 50 work properly then I can be X% confident that all 450 will work properly. Thanks very much for your help, maybe it's not possible.

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    Re: No Standard Deviation

    "functioning properly" is a yes or no response, sorry if my original post was a bit cryptic.

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    Re: No Standard Deviation


    hi,
    this would be something called a success run test.

    The probability of an item picked from your population functioning properly will be R = (1-CL)**(1/N) where CL is your confidence interval and N is the number of tested units, provided all N functioned properly.

    Regards
    rogojel

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