Classification: Basic Concepts

Classification of data is an important subject in chemometrics as evidenced by the large number of citations appearing in the Chemical Abstract database annually on supervised pattern recognition techniques. Developing a classifier from spectral or chromatographic data is desirable for any number of reasons including source identification, food quality testing, detection of odorants, presence of disease in a patient or animal from which a sample has been taken, and the detection of a specific analyte to name a few. However, in chemistry the scope of the analysis will often go beyond a simple classification of the data. Higher levels of classification for chemical data include but are not limited to detection of an unknown class in the training or validations set, the importance of individual measurement variables to the overall classification of the data, and the characterization of the internal class structure, for example, the presence of the asymmetric data structure in the training set.