When is an outlier not an outlier?

The tendency of the users of NIRS is to think of the composition particularly in terms of the reference data, for the prediction of which the technique is to be used. The concept and principle of NIRS analysis differ from classical chemical analysis in that NIRS is based exclusively on the spectra. Spectra are of course, derived from the chemical and physical make-up of the material, but the spectra can differ among materials that are reported as having the same chemical composition. This is particularly a factor with growing crops, and is exemplified in the article, which endorses the recommendation to take replicate samples of the same reported composition for calibration development