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[ai-geostats] Transformation of zero values for kriging

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  • Schlatter Christian
    Dear list-readers We were studying lepidopteran egg parasitism rates in a grid design (on 6 x 24 plants, totally 144) in the field. The idea was to detect
    Message 1 of 2 , Oct 25, 2005
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      Dear list-readers

      We were studying lepidopteran egg parasitism rates in a grid design (on 6 x 24 plants, totally 144) in the field. The idea was to detect influences in terms of directional dependencies of the parasitism rate (variograms), of base parasitism rate (nugget), and of “distance of the effects” (range).

      Now egg parasitism rate was quite low and rare due to different problems (meteorological, area, test site, spraying in field, etc) so we have an average of 10-20 % of parasitized eggs (out of 144 points). For some non-spatial statistical testing this was more or less ok.

      For the geostatistical work (I was thinking of universal kringing), the number of values is quite little. So I was thinking about transforming them by means of the exponential function (exp^zi), in order to get 144 values and to retransform the result.

       

      Can I proceed in this way or am I completely on the wrong way with this approach?

       

      Thank you very much for you attention.

       

      Best wishes

       

      Christian

       

      °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°

      Christian Schlatter

      GIS

      Pflanzenschutz: Schädlinge – Nützlinge

       

      Forschungsinstitut für biologischen Landbau (FiBL)

      Institut de recherche de l'agriculture biologique

      Istituto di ricerche dell'agricoltura biologica Research

      Institute of Organic Agriculture CH-5070 Frick , Switzerland

      Ackerstrasse

      CH- 5070 Frick

       

      christian.schlatter@...

       

      Telefon 0041 62 865 72 75

      Fax 0041 62 865 72 73

       

      Unsere Homepage:

      http://www.fibl.org

      http://www.biogene.org

      http://www.organicxseeds.com

      http://gis.fibl.ch/WWFMap/viewer.htm

      °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°

       

    • Pierre Goovaerts
      Hi Christian, It looks like your data are rates and consist of a numerator and denominator. In this case, you cannot apply common geostatistical tools since
      Message 2 of 2 , Oct 25, 2005
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        Hi Christian,

        It looks like your data are rates and consist of a numerator and denominator. In this case, you cannot apply common geostatistical tools since the reliability of your observations will vary depending on the number of eggs you have sampled for each plant.
        I am facing similar problems with cancer rates and have been using both Poisson kriging and binomial cokriging. A few papers are available on my webpage and I just submitted another paper that describes Poisson kriging in more details and provides the code to do the analysis. I would gladly share it with you once it is accepted, which should be very soon.

        Regards,

        Pierre

        Pierre Goovaerts
        Chief Scientist at Biomedware
        516 North State Street
        Ann Arbor, MI 48104
        Voice: (734) 913-1098
        Fax: (734) 913-2201
        http://home.comcast.net/~goovaerts/

        -----Original Message-----
        From: Schlatter Christian [mailto:christian.schlatter@...]
        Sent: Tue 10/25/2005 4:33 AM
        To: ai-geostats@...
        Cc:
        Subject: [ai-geostats] Transformation of zero values for kriging
        Dear list-readers

        We were studying lepidopteran egg parasitism rates in a grid design (on 6 x 24 plants, totally 144) in the field. The idea was to detect influences in terms of directional dependencies of the parasitism rate (variograms), of base parasitism rate (nugget), and of "distance of the effects" (range).

        Now egg parasitism rate was quite low and rare due to different problems (meteorological, area, test site, spraying in field, etc) so we have an average of 10-20 % of parasitized eggs (out of 144 points). For some non-spatial statistical testing this was more or less ok.

        For the geostatistical work (I was thinking of universal kringing), the number of values is quite little. So I was thinking about transforming them by means of the exponential function (exp^zi), in order to get 144 values and to retransform the result.



        Can I proceed in this way or am I completely on the wrong way with this approach?



        Thank you very much for you attention.



        Best wishes



        Christian



        °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°

        Christian Schlatter

        GIS

        Pflanzenschutz: Schädlinge - Nützlinge



        Forschungsinstitut für biologischen Landbau (FiBL)

        Institut de recherche de l'agriculture biologique

        Istituto di ricerche dell'agricoltura biologica Research

        Institute of Organic Agriculture CH-5070 Frick, Switzerland

        Ackerstrasse

        CH- 5070 Frick



        christian.schlatter@... <mailto:christian.schlatter@...>



        Telefon 0041 62 865 72 75

        Fax 0041 62 865 72 73



        Unsere Homepage:

        http://www.fibl.org <http://www.fibl.org/>

        http://www.biogene.org <http://www.biogene.org/>

        http://www.organicxseeds.com <http://www.organicxseeds.com>

        http://gis.fibl.ch/WWFMap/viewer.htm <http://gis.fibl.ch/WWFMap/viewer.htm>

        °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°
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