To aid interpretation, the O-PLS coefficients were plotted into a spectral domain using the back-scaling method (Cloarec et al, 2005). Using this method, the weights of each variable are back-scaled to their initial metric of the data and then the shape of NMR spectra and the sign of the coefficients are preserved. However, the weights of the variables can still be compared using a colour code corresponding to the square of the actual O-PLS coefficients. By construction, the O-PLS coefficients are directly proportional to the correlation coefficients between the discriminant axis and the NMR data. For this reason, the square of the coefficients can be represented in terms of correlation after applying the same corrective factor to all coefficients, allowing by this way an estimation of the amount of variance of each NMR variable involved in the discrimination.