Abstract
This paper discusses proportional odds model and similarity on the construction of Traditional Chinese Medicine (TCM) chronic gastritis syndrome model. The syndromes explain the true relationships among a set of symptoms, which can be characterized by marginal probabilities and conditional probabilities. The former represents the distribution of levels of the syndrome across the symptoms. The latter describes the probabilities of an individual in a certain syndrome being at a particular level of the symptom, so it enables us to characterize the nature of the syndromes and the essence of the symptoms. A graph model for TCM syndromes gives intuitive mathematical insight into its use and computation. Similarity among syndromes explains that the model we construct is altogether fitting and proper.