[R-sig-Geo] geoR Beta Estimates Not Equal to lm Coefficients: Why?

[Joshua Palmer]

Hello everyone,

I am using the excellent geoR package to perform Kriging with External
Drift.  As to be expected, for any given set of covariates, trend
coefficients I obtain performing least-squares regression in SAS equal those
coefficients obtained by using R's lm function.  However, those trend
coefficients do NOT match the estimates for the beta values when I run
krige.conv (or likfit or variofit) in geoR.  The coefficients are often
similar, but they are never nearly or exactly the same.  I was under the
assumption that geoR utilizes least-squares regression (on the trend.d
matrix) a la R's lm function to derive beta estimates.  This appears to be
incorrect.

Would anyone be able to explain to me why I am noting this difference or
should I be noting a difference?  I have researched R mailing lists and geoR
documentation but have been unable to find an answer.  Please let me know if
additional specificity is needed.  This dilemma is universal across
different sets of covariates and covariance models or parameters.

Any assistance is greatly appreciated and I thank you for your time.
Joshua Palmer
Meteorologist
Atlanta, GA, USA