Re: [R] Using R to process spectroscopic data

From: Bjørn-Helge Mevik <bhs2_at_mevik.net>
Date: Thu 09 Feb 2006 - 01:21:54 EST

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.

-- 
Bjørn-Helge Mevik

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Received on Thu Feb 09 01:40:06 2006

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