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Re: AI-GEOSTATS: Sequential simulation

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  • Pierre Goovaerts
    Hi, Your question is puzzling. First, you should clarify what you mean by zero inflated distribution. Second, a normal score transform should by construction
    Message 1 of 2 , Feb 16, 2004
      Hi,

      Your question is puzzling.
      First, you should clarify what you mean by zero inflated distribution.
      Second, a normal score transform should by construction always yield
      a set of normal scores with zero mean, hence it is unclear why you
      get an average of -1.
      Note that if your variable takes only a few values or if there is
      a large proportion of data below the detection limit or equal to zero,
      a normal score transform that artificially despikes these similar
      values might not be the most appropriate approach.

      Pierre Goovaerts

      <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

      Dr. Pierre Goovaerts
      President of PGeostat, LLC
      Chief Scientist with Biomedware Inc.
      710 Ridgemont Lane
      Ann Arbor, Michigan, 48103-1535, U.S.A.

      E-mail: goovaert@...
      Phone: (734) 668-9900
      Fax: (734) 668-7788
      http://alumni.engin.umich.edu/~goovaert/

      <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

      On Mon, 16 Feb 2004, [ISO-8859-1] José Manuel Blanco Moreno wrote:

      > Hi, list,
      > I'm working on simulation (again) with sgsim (gslib) and I've found
      > something that troubles me...
      > I'm trying to simulate a variable that has a zero inflated distribution
      > (weed counts), and I proceed as follows:
      > -calculate the normal scores variogram for that variable.
      > -fit the model (the total sill sums slightly more than one)
      > -especify the details for simulation ... and run it.
      >
      > And then comes the problem: in the debugging file appears a rather
      > pretty question asking if the variance is near one (when it is clear it
      > is not; my variance is about TWO!) and if the mean is near zero (when,
      > again, it is not near zero, but near minus one).
      > I suppose that this is generated by that zero inflated distribution.
      > Is that true?
      >
      > Another question; Could this affect the validity of simulation? Should I
      > proceed in another way (v.g. Indicator simulation)?
      >
      > Thank you for any light shed on this question.
      >
      > --
      > ---------------------------------------
      > José Manuel Blanco Moreno
      >
      > Dept. de Biologia Vegetal (Botànica)
      > Universitat de Barcelona
      > Av. Diagonal 645
      > 08028 Barcelona
      > SPAIN
      > ---------------------------------------
      >
      > phone: (+34)93.402.1471
      > fax: (+34)93.411.2842
      > e-mail: jmblanco@...
      >
      >
      >
      >
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