Dear list,
 
I have two problem and I would like to know you opinion.
 
1.  I am kriging 6 environmental variables, SO2, NOx, O3, CO, NO, PM10, to built and enviromental index in R. I have standardized the observed values and I am implementing in geoR  the function likfit to obtain the parameter lambda (Box-Cox transformation) to see if the standarized variables are normal. But I have error using the likfit function. 
It could be that the error arise because the standarized variables contain negative values?
 
2. I have values of the 6 variables at 25 locations but I want to use a linear combination of the six variables to deal with only a variable. Finally, I want to interpolate this only variable in several sites where I have not observed data. 
What do you think is better? 
- To interpolate each one of the six variables and then elaborate the linear combination.
- Or to elaborate a linear combination with the observed values and finally krige the linear combination.
 
Thanks in advance,
Gema Fernández-Avilés
 
Universidad de Castilla-La Mancha.
(Spain)


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