An index for deciding the necessity of surgically operating on the jaw in orthodontic treatment, an index for deciding disharmony of the maxilla and mandible in dental treatment, and an index for deciding dentofacial deformity. The distance (S-A) between S and A, the distance (S-B) between S and B and the distance (Go-Me) between Go and Me are measured by the cephalometric radiography of a patient. By using the distances, P=((S-B)+(Go-Me))/(S-A) is calculated by a processor. P is used as an index for deciding the necessity of surgically operating on the jaw in orthodontic treatment, an index for deciding disharmony of the maxilla and mandible in dental treatment, or an index for deciding dentofacial deformity. Instead of P, Q=(P−[P])×1000 ([ ] denotes Gausss symbol) (where 2.000≦P<3.000) or Q=(P−([P]+1))×1000 (where P<2.000) may be calculated by a processor and used.
