Dear Meng-Ying,
It's not that you are defining variance to be the variance of data to be data
beyond the range of the variogram. Say you have a panel made up of a
1 million samples which covers the entire panel, then you select 1000 samples
to estimate the variance. If two samples of the thousand are within range of
each other (close and similar value), then you are effectively doubling up
on one of the samples, so to give a better representation of the 1 million
samples you are better to remove the doubled up sample, giving 999
samples to estimate the variance of the 1 million. This will give a better
estimate of the variance you could calculate from the million by the least
squares classical method, which is what Isobel was saying.
Regards Digby
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