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Attribute Sample Size

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  • #31145

    CAR
    Participant

    Can someone please explain how to arrive at an appropriate attribute sample size in plain english???
    The total population is 1264 accounts. How many accounts are required to obtain a 95% confidence level and a +/- 5% margin of error?
    Thank you in advance.
    CAR
     
     
     

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    #81917

    lin
    Participant

    It depends on what you want the data to show you. If you are just looking for a sample of the population then 30 would be the number of choice, but if you are trying to detect a change between two sample then you need to know how small the change is. The smaller the change the more samples you will need.

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    #81918

    Chip Hewette
    Participant

    I think we can help, but we need more info.
    1.  What are you measuring within the 1264 accounts?
    2.  What do you want to know about that measurement?  The average value for the measurement from a sample within 1264 accounts?
    3.  Do you want to detect a 5 percentage point shift from an average historical value to a ‘new’ value?

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    #81919

    abasu
    Participant

    The formula that you are looking for is
    n = Z^2*(p)*(1-p)/(delta p)^2 where
    n = sample size
    Z = 1.96 for 95% confidence
    p = proportion rate (we know total population but not p)
    delta p = difference you want to detect (0.1 in this example)

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