The numerical approach to classification: a medical application to develop a typology for facial pain

Applications of numerical taxonomy in medicine are relatively rare. We describe an application in which a new typology is developed for the classification of pain distribution in patients with temporomandibular pain dysfunction syndrome. The methodology of the numerical approach is presented and key issues are highlighted, especially relating to validation of taxonomic structure. From the dendrogram obtained by Ward's hierarchical method, five pain groups are distinguished which relate systematically to anatomy and are clinically meaningful. Cluster structure is subjected to a battery of reproducibility tests and is found to be broadly reproducible for different algorithms and sub-samples of subjects. Finally, the new typology is shown to have heuristic value in providing fresh insight into the nature of a complex syndrome.