[R] Using R to process spectroscopic data

[Bjørn-Helge Mevik]

Dirk De Becker wrote:

> * Determine the range of the spectrum to be used -> For this, I should 
> be able to calculate the regression coefficients

You can get the regression coefficients from a PLSR/PCR with the
coef() function.  See ?coef.mvr  However, using the regression
coefficients alone for selecting variables/regions, can be 'dangerous'
because the variables are highly correlated.

One alternative is 'variable importance' measures, e.g. VIP (variable
importance in projections) as described in Chong, Il-Gyo & Jun,
Chi-Hyuck, 2005, Performance of some variable selection methods when
multicollinearity is present, Chemometrics and Intelligent Laboratory
Systems 78, 103--112.  A crude implementation of VIP can be found in
http://mevik.net/work/software/pls.html

Another alternative is to use jackknife-estimated uncertainties of the
regression coefficients in significance tests.  (I don't have any
reference or implementation, sorry. :-)

The correlation loadings can also give valuable information about
which variables that might be important for the regression.  See
?corrplot in the pls package.

-- 
Bjørn-Helge Mevik