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

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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 1 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
      >>
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      >
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