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1790Re: [ai-geostats] F and T-test for samples drawn from the same p

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  • Chaosheng Zhang
    Dec 6, 2004
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      Good idea, and that's a step forward. Any references or is it still an idea?



      ----- Original Message -----
      From: "Isobel Clark" <drisobelclark@...>
      To: "AI Geostats mailing list" <ai-geostats@...>
      Sent: Monday, December 06, 2004 1:07 PM
      Subject: Re: [ai-geostats] F and T-test for samples drawn from the same p

      > Dear all
      > I am having difficulty understanding why none of you
      > want to try a spatial approach to statistics. Everyone
      > is trying to make the 'independent' statistical tests
      > work on spatial data. Try turning this around and look
      > at the spatial aspect first.
      > (1) Testing variances: the sill on the semi-variogram
      > (total height of model) is theoretically a good
      > estimate for the sample variance when auto-correlation
      > or spatial dependence is present. Do your F test on
      > that. Yes, you still have degrees of freedom problems,
      > but with thousands of samples the 'infinity column'
      > should be sufficient.
      > (2) Testing means: the classic t-test in the presence
      > of 'equal variances' requires the 'standard error' of
      > each mean. For independent samples, this is s/sqrt(n).
      > For spatially dependent samples, this is the kriging
      > standard error for the global mean. Your only problem
      > then is getting a global standard error.
      > Isobel
      > http://geoecosse.bizland.com/whatsnew.htm


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