AI-GEOSTATS: relatively high semivariances at first lags

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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
Message 1 of 2 , Apr 15, 2002
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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• 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
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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