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Math Help - Comparing two data

  1. #1
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    Comparing two data

    Hi,
    Could anyone suggest a way to compare the following two set of data
    data 1 :
    Mean average=54.7 gram
    standard deviation = 1.1 gram
    x=50

    Data 2:
    Mean average=50.3 gram
    standard deviation = 3.7 gram
    x=50

    I have tried the normal distribution on the first set of data only to end up getting z score of -4.27 ,I can change this to positive but the z score table end with 3-4 maximum limit
    Is there any other method to compare these two set of data?
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  2. #2
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    Re: Comparing two data

    Quote Originally Posted by nova12 View Post
    Hi,
    Could anyone suggest a way to compare the following two set of data
    data 1 :
    Mean average=54.7 gram
    standard deviation = 1.1 gram
    x=50

    Data 2:
    Mean average=50.3 gram
    standard deviation = 3.7 gram
    x=50

    I have tried the normal distribution on the first set of data only to end up getting z score of -4.27 ,I can change this to positive but the z score table end with 3-4 maximum limit
    Is there any other method to compare these two set of data?
    Not exactly sure what you are trying to do here.

    Are you trying to do a hypothesis test that these two sets of data came from the same underlying distribution or not?

    Are you trying to decide which of the two underlying distributions x is most likely to have come from?
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  3. #3
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    Re: Comparing two data

    You should use the pooled standard deviation instead of just using 1.1 if you do that you should get a more reasonable z value.
    Thanks from nova12
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  4. #4
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    Re: Comparing two data

    Quote Originally Posted by romsek View Post
    Not exactly sure what you are trying to do here.

    Are you trying to do a hypothesis test that these two sets of data came from the same underlying distribution or not?

    Are you trying to decide which of the two underlying distributions x is most likely to have come from?
    Yeah am trying to figure out you second suggestion.
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  5. #5
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    Re: Comparing two data

    Quote Originally Posted by nova12 View Post
    Yeah am trying to figure out you second suggestion.
    Since the two sets of data are from different underlying distributions I can't agree with Shakarri.

    If all you want to do is decide between the two distributions then simply select the one with the largest z-score.

    $\left(\dfrac {50-54.7}{1.1}\right)=-4.27$
    $\left(\dfrac{50-50.3}{3.7}\right)= -0.27$

    $-0.27 > -4.27$ and thus it is more likely that your sample came from the second distribution.

    The corresponding probabilities are

    $Pr[-4.27] = 9.77x10^{-6}$

    $Pr[-0.27] = 0.39$
    Thanks from nova12 and Shakarri
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  6. #6
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    Re: Comparing two data

    Quote Originally Posted by romsek View Post
    Since the two sets of data are from different underlying distributions I can't agree with Shakarri.

    If all you want to do is decide between the two distributions then simply select the one with the largest z-score.
    Oh you are right, I read it as 50 being the sample size for each distribution and I thought he was seeing if the two sets of data were from the same distribution
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