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[ai-geostats] Search neighbourhood, conditional bias, etc

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  • Collier, Perry (TS)
    Hi List Maybe this topic has been done to death, but I d like to poke the carcass if I may... Edward Isaaks via AI (15 February 2006) said of a paper by Van et
    Message 1 of 1 , May 1, 2006
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      Hi List

      Maybe this topic has been done to death, but I'd like to poke the
      carcass if I may...

      Edward Isaaks via AI (15 February 2006) said of a paper by Van et al on
      kriging neighbourhood analysis:

      "..a paper...that actually proposes a method for designing the kriging
      search neighborhood based on minimizing conditional bias. Horrifying -
      do they not realize that such practice actually increases the estimation
      error of the predicted tonnes and grade above cutoff? This paper is
      probably the worst (best?) example I have seen of a faulty misconception
      in 25 years of ore resource assessment. One can almost understand why
      geostatistics might be labeled a scam."

      This view is also shared by some of my colleagues and acquaintances, but
      then on the other hand some consulting houses compute the statistics
      outlined in this paper (slope of regression, weight of the SK mean etc)
      and others such as "kriging efficiency" as a matter of course - are they
      barking up the wrong tree or are these statistics helpful in certain
      circumstances?

      Ed also said "...in mining applications (where geostatistics has its
      roots) conditional bias is actually irrelevant, unless the estimates are
      used for grade control"

      Can we, for the benefit of my embryonic but inquisitive geostatistical
      mind, thrash out this topic - the pros and cons of conditional bias -
      when is it good, when is it bad (ie: need to minimise it), how do you
      quantify it, how does minimising conditional bias increase estimation
      error, what is the importance of the search neighbourhood and sample
      selection, means of determining the best size/orientation etc...and why
      is there the apparent lack of unity of opinion on this issue?

      Speak to me gurus!

      Cheers

      Perry Collier
      Senior Geologist
      Rio Tinto OTX
      Phone: +61 7 3327 7676
      Mobile: 0408 015 837
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