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GEOSTATS: Summary 2 on the decomposition of the nugget effect

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  • Gregoire Dubois
    Dear all, two other replies I got to my question on the decomposition of the nugget effect that I have forgotten to put in my first summary can be found
    Message 1 of 1 , Sep 21, 1905
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      Dear all,

      two other replies I got to my question on the decomposition of the nugget
      effect that I have forgotten to put in my first summary can be found
      hereafter.

      From Guillaume Larocque

      " I am not a geostats expert, but I have a little problem with the definition
      of the Nugget you mentioned. If we suppose that the Nugget is the value at 0
      plus a very small distance, it is like saying that our model is not adequate
      at the micro scale. To me, the definition of the Nugget that says NE=MV+EV is
      valid only if we say the Nugget is the value at the smallest lag for which we
      have pairs of observations. If we have confidence in our sampling scheme and
      model, than I think we should say that the Nugget effect at a value close to
      zero is only the error variance. If not, then it is really hard to distinguish
      between MV and EV.

      I think the Nugget is a ill-defined concept and I hope there will be a good
      discussion about it on the list."


      From Paulo Justiniano Ribeiro Jr
      "About the nugget effect I'm surprised with you results.
      You should see a difference between the estimates only at data locations.

      When the nugget is regarded as being erros variance the interpolated
      surface is smooth. When it is regarded as micro-variance you should see
      exactly the same surface except for the data locations where you will find
      some "spikes" corresponding to the data. When you split the nugget the spike
      will be proportional to amout of nugget regarded as being the
      micro-variance."

      He also sent me two files to illustrate his comments

      - nugget.ps: plots with kriging results in a 1-D problem with
      3 options for nugget: 0%, 100% and 50% of microscale variance

      - nugget.example: the code in geoR/geoS to produce the plot

      Thanks again to all,

      Regards

      Gregoire


      Gregoire Dubois
      Section of Earth Sciences
      Institute of Mineralogy and Petrography
      University of Lausanne
      Switzerland

      Currently detached in Italy

      http://curie.ei.jrc.it/ai-geostats.htm

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