Dear all,

two other replies I got to my question on the decomposition of the nugget

effect that I have forgotten to put in my first summary can be found

hereafter.

From Guillaume Larocque

" I am not a geostats expert, but I have a little problem with the definition

of the Nugget you mentioned. If we suppose that the Nugget is the value at 0

plus a very small distance, it is like saying that our model is not adequate

at the micro scale. To me, the definition of the Nugget that says NE=MV+EV is

valid only if we say the Nugget is the value at the smallest lag for which we

have pairs of observations. If we have confidence in our sampling scheme and

model, than I think we should say that the Nugget effect at a value close to

zero is only the error variance. If not, then it is really hard to distinguish

between MV and EV.

I think the Nugget is a ill-defined concept and I hope there will be a good

discussion about it on the list."

From Paulo Justiniano Ribeiro Jr

"About the nugget effect I'm surprised with you results.

You should see a difference between the estimates only at data locations.

When the nugget is regarded as being erros variance the interpolated

surface is smooth. When it is regarded as micro-variance you should see

exactly the same surface except for the data locations where you will find

some "spikes" corresponding to the data. When you split the nugget the spike

will be proportional to amout of nugget regarded as being the

micro-variance."

He also sent me two files to illustrate his comments

- nugget.ps: plots with kriging results in a 1-D problem with

3 options for nugget: 0%, 100% and 50% of microscale variance

- nugget.example: the code in geoR/geoS to produce the plot

Thanks again to all,

Regards

Gregoire

Gregoire Dubois

Section of Earth Sciences

Institute of Mineralogy and Petrography

University of Lausanne

Switzerland

Currently detached in Italy

http://curie.ei.jrc.it/ai-geostats.htm
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