[R] Spatial regression
bbolker at gmail.com
Tue Jul 31 18:01:02 CEST 2012
DanielFV <kalandru <at> hotmail.com> writes:
> I conducted GLS analyses introducing variance structures and correlation
> structures to improve the model.
> I plotted variograms before and after adding the correlation structures but
> I would like to be able to conduct a test that gives me actual values for
> spatial autocorrelation, so that I can show whether adding the correlation
> structures improved significantly the model.
> My variograms do not seem to improve after adding the correlation structures
> so I don't know if I am conducting the right analyses.
One thing to watch out for is that you want to extract the residuals
with type="normalized" (see ?residuals.lme) (or use resType="normalized"
in ACF() or Variogram: see ?acf.GLS, ?Variogram.GLS) --
otherwise, your residuals will be "pearson"
type, corrected for non-homogeneous variance but not for correlation
(I have fallen into this trap myself).
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