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Thread: Difference in proportion for large sample size

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    Difference in proportion for large sample size




    Hi,

    I have 2 proportions from 2 years:
    P1(2001): 11000/12500 = 88.0%
    P2 (2002): 11500/12800 = 89.8%

    I am interested in knowing if there is a statistical increase in % from 2001 to 2002. So, H0 = P1-P2>0; H1 = P1-P2 < 0

    I had applied z-test to this problem and it gave a significant result. Is this true?

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    Re: Difference in proportion for large sample size

    Yes, at such large sample sizes even minute differences will be significant. The question is, is this practically relevant?

    regards

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    Re: Difference in proportion for large sample size

    Thanks for the reply. Will think about it. =)

    Is there another method for comparing proportions for large sample size?

    I have another set of %
    Pre: (sample proportion) 6000/10000 = 60%
    Post: (population proportion) 70000/100000 = 70%

    Would it be correct to do a one way z-test using post 0.7 as expected value?

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    Re: Difference in proportion for large sample size


    hi,
    sure, but you will get the same problem - you need domain knowledge to decode if the difference is important or not, as opposed to significant

    regards

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