Dear Roger,
 
Thank you very much for your answers. I tried repeated 10-fold crossvalidation on both the SAR and CAR family with predictions based on only the aspatial terms. SAR yields prediction errors a bit smaller as a plain lm model. The prediction errors with the CAR family are huge. So I assume that predictions based on the aspatial terms are not working well for the CAR family.
 
Regards,
 
Thierry

----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx@inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey




________________________________

Van: Roger Bivand [mailto:Roger.Bivand@nhh.no] 
Verzonden: zaterdag 11 april 2009 23:23
Aan: ONKELINX, Thierry; r-sig-geo@stat.math.ethz.ch
CC: Roger Bivand
Onderwerp: SV: [R-sig-Geo] Questions about spautolm


Wrt. question 1 - use a symmetric style, for example B or C, not W (row standardisation). CAR should not be used with asymmetric weights.

Wrt. question 2 - no, there are no prediction methods for spautolm output objects, but the predictions would be
the product of the aspatial coefficient estimates and the newdata values, as in the case of the predictions for SAR errorsarlm objects for newdata. The spatial coefficient affects the residual, so will impact the variance of the prediction rather than the point estimate (I believe). There is a discussion in Kaluzny et al. 1998 - the S-Plus spatial stats module book.

Hope this helps,

Roger

--- Roger Bivand, NHH, Helleveien 30, N-5045 Bergen, Roger.Bivand@nhh.no

________________________________

Fra: r-sig-geo-bounces@stat.math.ethz.ch på vegne av ONKELINX, Thierry
Sendt: lø 11.04.2009 17:47
Til: r-sig-geo@stat.math.ethz.ch
Emne: [R-sig-Geo] Questions about spautolm



Dear all,

I have a few questions about spautolm from the spdep package.

I get warning about "Assymetric weights" with family = "CAR". The
weights are defined like the code below. The dataset is roughly based on
a 1000 x 500m grid. But only the gridpoints in forest are measured.
Hence it is not possible to get symmetric weights. Is this violating an
assumuption of the model? Or can this cause another problem?

Buren <- dnearneigh(cbind(dataset$X, dataset$Y), d1 = 0, d2 = 6500)
Weights <- nb2listw(Buren, style = "W", zero.policy = TRUE)

My second question is about prediction. Is it possible to use a spautolm
model to make predictions for other locations?

Regards,

Thierry

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx@inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

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Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer 
en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is
door een geldig ondertekend document. The views expressed in  this message
and any annex are purely those of the writer and may not be regarded as stating 
an official position of INBO, as long as the message is not confirmed by a duly 
signed document.

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