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AI-GEOSTATS: relatively high semivariances at first lags

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  • Ercan Yesilirmak
    Dear list members My question is as follows: In my exercise, semivariance value is at near zero high at first lag, then in second lag jumps to the highest
    Message 1 of 2 , Apr 15, 2002
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      Dear list members

      My question is as follows:

      In my exercise, semivariance value is at near zero
      high at first lag, then in second lag jumps to the
      highest semivariance value, and then decreases
      gradually to global variance and fluactuates around
      it. These data is logtransformed form of a data with a
      skewness of 3.9. Variogram is omnidirectional. Data is
      composed of 34 samples.

      Where is the problem? How to solve this?

      Regards
      Ercan

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    • Chaosheng Zhang
      Ercan, There might be two problems in your data set. (1) The sample number is too small. (2) The are some high value outliers in your data set. I understand
      Message 2 of 2 , Apr 15, 2002
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        Ercan,

        There might be two problems in your data set.
        (1) The sample number is too small.
        (2) The are some high value outliers in your data set.

        I understand that it is hard for you to improve the first problem. However,
        the second problem can be partly solved by (1) excluding the outliers in the
        variogram calculation; (2) a better transformation (e.g., Box-Cox); (3) use
        of median values instead of the average in the variogram calculation. The
        highest value at the first lag is caused by some pairs of significant
        variance at very short distances (one of the values in these pairs should be
        regarded as a spatial outlier).

        Good luck.

        Chaosheng Zhang
        =================================================
        Dr. Chaosheng Zhang
        Lecturer in GIS
        Department of Geography
        National University of Ireland
        Galway
        IRELAND

        Tel: +353-91-524411 ext. 2375
        Fax: +353-91-525700
        Email: Chaosheng.Zhang@...
        ChaoshengZhang@...
        Web: http://www.nuigalway.ie/geography/zhang.html
        =================================================

        ----- Original Message -----
        From: "Ercan Yesilirmak" <ercanyesilirmak@...>
        To: <ai-geostats@...>
        Sent: Monday, April 15, 2002 8:59 AM
        Subject: AI-GEOSTATS: relatively high semivariances at first lags


        > Dear list members
        >
        > My question is as follows:
        >
        > In my exercise, semivariance value is at near zero
        > high at first lag, then in second lag jumps to the
        > highest semivariance value, and then decreases
        > gradually to global variance and fluactuates around
        > it. These data is logtransformed form of a data with a
        > skewness of 3.9. Variogram is omnidirectional. Data is
        > composed of 34 samples.
        >
        > Where is the problem? How to solve this?
        >
        > Regards
        > Ercan
        >
        > __________________________________________________
        > Do You Yahoo!?
        > Yahoo! Tax Center - online filing with TurboTax
        > http://taxes.yahoo.com/
        >
        > --
        > * To post a message to the list, send it to ai-geostats@...
        > * As a general service to the users, please remember to post a summary of
        any useful responses to your questions.
        > * To unsubscribe, send an email to majordomo@... with no subject and
        "unsubscribe ai-geostats" followed by "end" on the next line in the message
        body. DO NOT SEND Subscribe/Unsubscribe requests to the list
        > * Support to the list is provided at http://www.ai-geostats.org


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