This comment relates to the unbiasedness constraints of the cokriging system. In ordinary cokriging, the sum of the secondary data weights is forced to be equal to zero, hence if only secondary data are used in the estimation (i.e. if no data for the variable of interest or primary variable are found in the search window) the estimator has an expected value of zero and so will lead to a biased estimation... In the case of simple cokriging, if no primary data are found in the search window, a weight of one is assigned to the global mean of the primary variable which is added to the weighted sum of secondary data. Hope it helps.... Pierre Pierre Goovaerts Chief Scientist at BioMedware Inc. Courtesy Associate Professor, University of Florida President of PGeostat LLC Office address: 516 North State Street Ann Arbor, MI 48104 Voice: (734) 913-1098 (ext. 8) Fax: (734) 913-2201 http://home.comcast.net/~goovaerts/
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