Fig. 4.

(a) Selectivity ratio multiplied by the sign of the correlation vector (bottom) for POX-PLS model compared to the first derivative, mean centered spectra of POX and PenV (vector normalized). (b) Selectivity ratio multiplied by the sign of the correlation vector (bottom) for PenV-PLS model compared to the first derivative, mean centered spectra of POX and PenV (vector normalized). A high absolute value of the selectivity ratio points to spectral regions that have a strong influence on the model, while the sign indicates whether the correlation is positive or negative.