Hello, The nugget effect is usually interpreted as a combination of small-scale variability and measurement errors. The only way to distinguish between both is to assess the magnitude of measurement errors in the lab, e.g. through replication of the measurement on subsamples. Wherever the interpolated node does not coincide with a sampled location, the nugget variance is filtered. So, I don't see how you could compare the common kriging with factorial kriging in a cross-validation mode. Regards, Pierre Pierre Goovaerts Chief Scientist at BioMedware 516 North State Street Ann Arbor, MI 48104 Voice: (734) 913-1098 (ext. 8) Fax: (734) 913-2201 http://home.comcast.net/~goovaerts/
________________________________ From: M. Nur Heriawan [mailto:[EMAIL PROTECTED] Sent: Mon 3/6/2006 8:39 PM To: [email protected] Subject: RE: [ai-geostats] kriging without a nugget Dear Pierre, You mentioned that the nugget effect represents measurement errors or small-scale variability in the field. How to differentiate between both of them? Last year I was studying about factorial kriging. Actually on that time I wanted to use factorial kriging to filter the nugget variance. I assumed that my nugget variance only represented small-scale variability, because I was sure (I already checked) that my data set did not have any measurement errors. I also was surprised when I got the estimation result. Beforehand I guessed that the estimation result will be more precise as I excluded the nugget variance, but actually the result showed the contrary. When I plotted the estimated versus real values, the correlation coefficient was much less (compared to include the nugget variance in estimation). Thank you. Nur Heriawan ------------ Earth Resources Exploration Research Group Institut Teknologi Bandung Indonesia --- Pierre Goovaerts <[EMAIL PROTECTED]> wrote: > Hi Niklas, > > This is a very good question; in fact one of the > participants to my last short course > asked the same question since he was using ARCview > with the option > "nugget effect excluded" and was surprised to see > that his observations were > not honored by the kriging predictions. M. Nur Heriawan http://www.mining.itb.ac.id/heriawan __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
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