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Re: AI-GEOSTATS: Kriging with External Drift

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  • Nicholas Lewin-Koh
    Hi, Just to add to that Gotway and cressie I can t remember the exact citation did a large simulation study and showed that the bias from using the residual
    Message 1 of 13 , Dec 8, 2001
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      Hi,
      Just to add to that Gotway and cressie I can't remember the exact citation
      did a large simulation study and showed that the bias from using the
      residual variogram is very small in most cases.

      Nicholas

      On Fri, 7 Dec 2001 sshibli@... wrote:

      >
      > On Friday, December 7, 2001, at 10:05 AM, Andreas Hartmann wrote:
      > >
      > > How do I compute the residual semivariogramm when I don't know the
      > > residuals? Or have I misunderstood something in the concept of external
      > > drift?
      >
      > There is a nice section (Chapter 5.4) in Cressie's textbook (Statistics
      > for
      > Spatial Data) that discusses the potential bias of estimating
      > semivariograms from residuals and Matheron's formulation of
      > IRF-K kriging as an alternative means to krige in the presence of
      > a trend. The iterative fitting of the covariance is usually
      > non-graphical,
      > which is a drawback in itself, and Fig. 5.1 in the same section shows
      > Cressie's bold attempt at showing the pitfalls of doing such an
      > "automatic" fit. I have not used IRF-K kriging very much in practice,
      > for the above reasons. Better to live with the devil that I know, i.e.
      > my -- albeit biased -- residual variogram.
      >
      > Regards,
      >
      > Syed
      >
      >
      >
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      CH3
      |
      N Nicholas Lewin-Koh
      / \ Dept of Statistics
      N----C C==O Program in Ecology and Evolutionary Biology
      || || | Iowa State University
      || || | Ames, IA 50011
      CH C N--CH3 http://www.public.iastate.edu/~nlewin
      \ / \ / nlewin@...
      N C
      | || Currently
      CH3 O Graphics Lab
      School of Computing
      National University of Singapore
      The Real Part of Coffee kohnicho@...


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