[R-sig-Geo] Problem with BCtransform?

Ruben Roa RRoa at fisheries.gov.fk
Tue May 3 13:44:05 CEST 2005


Hi:

In geoR, when using BCtransform to back-transform the beta parameter into the 
space of the original data, like in

>mean(BCtransform(rnorm(5000,mean=likfitobject$beta,sd=sqrt(likfitobject$beta.var)),lambda=XXX,inverse=TRUE))

i have noticed (in two applications) that the value of this mean is much smaller (2.3 and 3.4 times smaller) than
the mean of the kriged predictions, obtained with

>mean(krig.object$predict)

even though geoR performs the back-transformation before kriging.

I would have thought that the two means (from back-transformed beta and from kriged predictions) would be
fairly similar. Of the two means the one that is closer to the mean of the raw data is the mean of the kriged 
predictions so i wonder maybe there is some problem with the BCtransform function when called by the
user? Or maybe there is something fundamental that i don't understand about the beta parameter (and thus its
back-transform)?

Thanks for clarifications.

Ruben




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