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Sample Size

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  • #36861

    John in Texas
    Participant

    I have 5000 item numbers in inventory.  I need to calculate a sample size of items to count (inventory) to assure the results (dollars variance) will be a representation of the population with 95% confidence.  I can risk a .5% error rate. Any suggestions?
    Thanks, John

    0
    #107350

    Tierradentro
    Participant

    No one has replied, is more information required?

    0
    #107356

    Bob J
    Participant

    Hi John,
    Yes, to calculate the sample size you need your average error rate (%).  Given that, the formula you need is:
    n=p(1-p)(Z/E)squared
    where:
    p=average error rate (?)
    Z = number of standard deviations associated with your confidence (in this case 1.96)
    E = allowed error (0.5%)
    Best Regards,
    Bob J

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    #107357

    John,
    You might like to take a look at a sample size calculator. One can be found at:
    http://www.surveysystem.com/sscalc.htm
    Of course, this approach assumes that all your items have the same value. Since you want to calculate a Dollar variance, you might want to do it by ‘value categories’. In other words, if a category has a high value, you might want to consider adjusting your confidence intervals accordingly.
    Andy

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    #107390

    Tierradentro
    Participant

    Thanks Bob!!
    The average error rate was .25

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