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RE: AI-GEOSTATS: In need of some help.

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  • Tom Nolan
    Harland, You could use the exact form of the Wilcoxon Rank Sum test, which is appropriate for sample sizes of 10 or less per group. Computational details are
    Message 1 of 7 , Dec 28, 2000
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      Harland,

      You could use the exact form of the Wilcoxon Rank Sum test, which is
      appropriate for sample sizes of 10 or less per group. Computational details
      are shown on p. 120 of "Statistical Methods in Water Resources," Helsel and
      Hirsch, 1992, Elsevier. The test is commonly used to determine whether two
      groups are from the same population (i.e. have the same median and other
      percentiles), or alternatively whether the medians are different.

      Tom Nolan

      > -----Original Message-----
      > From: ai-geostats-list@... [mailto:ai-geostats-list@...]On
      > Behalf Of mercury1@...
      > Sent: Tuesday, December 19, 2000 12:08 PM
      > To: ai-geostats@...
      > Subject: AI-GEOSTATS: In need of some help.
      >
      >
      >
      > Hi Folks!
      > This is my first post to this list. Hope it is not out of place.
      > I need a
      > way to compare two small populations (very small sample sizes..5
      > and 6....both
      > of which lack normality). I would like to compare them based on
      > 3-5 parameters.
      > Because of the above limitations I have given up on the validity
      > of a t-test
      > (which assumes a normal distribution and larger sample sizes).
      > My basic question
      > is this: are these two small populations statistically different
      > or do they
      > belong to the same population? I have asked many elementary
      > level stats folks
      > and have not been entirely satisfied with their solutions. So, I
      > pose this
      > 'problem' to you.
      > Thanks for your time.
      > Happy Holidays!
      > -Harland
      >
      > --
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      --
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    • Syed Abdul Rahman Shibli
      With five to six samples per population, concluding anything from the tests would really be pushing it. Complementing the results with any deterministic
      Message 2 of 7 , Dec 28, 2000
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        With five to six samples per population, concluding
        anything from the tests would really be pushing it.
        Complementing the results with any deterministic
        knowledge of the underlying population (genesis,
        noteworthy features, prior experience, etc) could lend
        some measure of validity to what you will eventually
        conclude from such tests (i.e. do they make sense).

        Unfortunately, doing that often leaves one in the
        unsavory position of realizing that there is more
        uncertainty than first thought of. Somewhat counter-intuitive,
        but so true in my personal experience.

        Syed

        -----Original Message-----
        From: Tom Nolan <btnolan@...>
        To: <ai-geostats@...>
        Date: Thursday, December 28, 2000 10:41 PM
        Subject: RE: AI-GEOSTATS: In need of some help.


        >Harland,
        >
        >You could use the exact form of the Wilcoxon Rank Sum test, which is
        >appropriate for sample sizes of 10 or less per group. Computational
        details
        >are shown on p. 120 of "Statistical Methods in Water Resources," Helsel and
        >Hirsch, 1992, Elsevier. The test is commonly used to determine whether two
        >groups are from the same population (i.e. have the same median and other
        >percentiles), or alternatively whether the medians are different.
        >
        >Tom Nolan
        >
        >> -----Original Message-----
        >> From: ai-geostats-list@... [mailto:ai-geostats-list@...]On
        >> Behalf Of mercury1@...
        >> Sent: Tuesday, December 19, 2000 12:08 PM
        >> To: ai-geostats@...
        >> Subject: AI-GEOSTATS: In need of some help.
        >>
        >>
        >>
        >> Hi Folks!
        >> This is my first post to this list. Hope it is not out of place.
        >> I need a
        >> way to compare two small populations (very small sample sizes..5
        >> and 6....both
        >> of which lack normality). I would like to compare them based on
        >> 3-5 parameters.
        >> Because of the above limitations I have given up on the validity
        >> of a t-test
        >> (which assumes a normal distribution and larger sample sizes).
        >> My basic question
        >> is this: are these two small populations statistically different
        >> or do they
        >> belong to the same population? I have asked many elementary
        >> level stats folks
        >> and have not been entirely satisfied with their solutions. So, I
        >> pose this
        >> 'problem' to you.
        >> Thanks for your time.
        >> Happy Holidays!
        >> -Harland
        >>
        >> --
        >> * To post a message to the list, send it to ai-geostats@...
        >> * As a general service to the users, please remember to post a
        >> summary of any useful responses to your questions.
        >> * To unsubscribe, send an email to majordomo@... with no
        >> subject and "unsubscribe ai-geostats" followed by "end" on the
        >> next line in the message body. DO NOT SEND Subscribe/Unsubscribe
        >> requests to the list
        >> * Support to the list is provided at http://www.ai-geostats.org
        >
        >
        >--
        >* To post a message to the list, send it to ai-geostats@...
        >* As a general service to the users, please remember to post a summary of
        any useful responses to your questions.
        >* To unsubscribe, send an email to majordomo@... with no subject and
        "unsubscribe ai-geostats" followed by "end" on the next line in the message
        body. DO NOT SEND Subscribe/Unsubscribe requests to the list
        >* Support to the list is provided at http://www.ai-geostats.org


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