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GS+ h-Scattergram Analysis

In an h-Scattergram the individual values that make up a semivariance pair (the head value and the tail value) are plotted against each other for all the points that make up a variogram lag class. Like variance cloud graphs, h-Scattergrams are very useful for discovering outliers that can skew the average semivariance value for a particular lag class. By placing the mouse on top of individual points you can determine which pairs of points in the data set are suspect.

h-Scattergrams are specific to both direction (isotropic or a specific anisotropic direction) and to a particular lag class. In the example below the scattergram is specific to the 7th lag class of the isotropic variogram, as noted in the graph title, and the mouse is on top of a pair made up of data records 4 and 92, which are separated by 52.28 distance units.  If you were to put the mouse over nearby points, you would learn that all the other points have record 4 in common.  This suggests that record 4 is an outlier and might be excluded from subsequent analysis (as described below).

h-Scattergrams are created by clicking on a point in a variogram or autocorrelogram in either the Autocorrelation Analysis window or the Variogram window. The List Values command lists numeric values for the cloud pairs in a separate h-Scattergram Listing window.
 

   images\h_scattergram_outlier_present.gif
   

Clicking on an outlier point brings up a sample mask dialog, from which it is easy to remove one of the data records making up a pair from the analysis. When one removes only record 4 from the above analysis, for example, all of the outlying pairs disappear:
 

   images\h_scattergram_outlier_removed.gif

 

 
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