Application of latent root regression for calibration in near-infrared spectroscopy. Comparison with principal component regression and partial least squares

Several analytical applications of spectroscopy are based on the assessment of a linear model, linking laboratory values to spectral data. Among various procedures, the following three methods have been used, i.e. principal component regression (PCR), partial least squares (PLS) and latent root regression (LRR). These methods can be applied in order to tackle the high collinearity commonly observed with spectral data. A collection of 99 near-infrared spectra, each including 351 data points, was used for the comparison of the 3 methods. The dependent variable was the specific production of pelleting. The spectral collection was divided into 49 and 50 observations for calibration and validation, respectively. The main elements of comparison were the minimum error observed on the verification set, the number of regressors introduced in the models and the stability of the errors around the minimum values. The minimum errors were 3.29, 3.13 and 3.07 for PCR, PLS and LRR, respectively. LRR required a large number of regressors in order to obtain the minimum error. Nevertheless, it gave very stable results, and the errors were not markedly increased when an arbitrary large number of regressors was introduced into the LRR model.