Calibration and validation of the NIRS data were performed using
The Unscrambler® programme (version 8.5.0, Camo, Trondheim,
Norway). The detection of anomalous spectra was accomplished using
the Mahalanobis distance (H-statistic) to the centre of the population,
which indicates how different a sample spectrum is from the average
spectrum of the set (Williams & Norris, 2001). A sample with an H
statistic of ≥3.0 standardised units from the mean spectrum was
defined as a global H outlier and was eliminated from the population.
In addition, some samples were removed from the initial data set as
concentration outliers (T-statistic), which measures how closely the
reference value matches the predicted value.