AI-GEOSTATS: bounds of IK variograms

[Dilling, Jörg]

dear all,

i have performed indicator kriging with different thresholds (corresponding
to 10th percentiles). is it correct that the variogram of each
xth-percentile is bounded to:

max cov = xth_percentile* (1-xth_percentile) ??

e.g. max cov (30th perc.) =  0.21, max.cov (90th perc.) = 0.09


thanks for comments

regards
jörg

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Re: AI-GEOSTATS: bounds of IK variograms

[Isobel Clark]

Jörg

Don't confuse indicator variables with classical
correlation coefficients. 

The maximum possible on your semi-variogram will be
where all differences are 1. That is every pair is
(1-0). And, of course, divided by 2. So the absolute
maximum an indicator semi-variogram can show is 0.5. 

Computationally then, if 90% of your data are 1s and
10% are zeroes, the semi-variogram can still
(theoretically) reach 0.5 if the 90% are all clustered
and the 10% are, say, peripheral.

Isobel
http://uk.geocities.com/drisobelclark


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