1. A method of calculating an index related to at least one of orthodontic treatment, dental treatment, and dentofacial deformity, the method comprising: receiving input, by a processing device, of points of measurement from a cephalometric radiogram, the points of measurement comprising: “S” representing Sella, a central point of the pot-shaped shaded image of the sella turcica of the sphenoid bone; “A” representing the deepest point on the median sagittal plane between the forefront of the anterior nasal spine, which is on the forefront part of the palatine shelf of maxilla and the Prosthion, which is the most frontal point of an alveolar process between the upper central incisors; “B” representing the deepest point between the infradentale, the most front point of the alveolar process between the lower central incisors and pogonion; “Go” representing Gonion, a cross point of the angle of the mandible and the bisector of the cross angle between the line connecting the posterior plane of the head of the temporomandibular joint and the posterior part of the angle of the mandible and the mandibular plane; “Pog” representing Pogonion, the most protruding point of protuberantia mentalis of the mandible for the Frankfort plane; “Gn” representing Gnathion, a cross point of the bone edge image of protuberantia mentalis and the bisector of the angle between the facial plane and the mandibular plane, where the facial plane is the line connecting “N” and Pog, with “N” representing the front point of the frontal suture of the nasal bone; “Me” representing the menton, the lowest point of the median section image of a chin; measuring, by a processing device, distances comprising: (S−A) representing the distance between points S and A; (S−X i ) representing the distance between points S and X i ; and (Go−X j ) representing the distance between points Go and X j , wherein i and j are each an integer from 1 to 4 and may or may not be equal to each other, with X 1 =B, X 2 =Pog, X 3 =Gn and X 4 =Me; and calculating, by a processing device, P=((S−X i )+(Go−X j ))/(S−A), for all combinations of i and j excluding the case of X i =B (i=1) and X j =Me (j=4), wherein the index is for at least one of deciding the necessity of surgically operating on the jaw in orthodontic treatment, deciding disharmony of the maxilla and mandible in dental treatment, and deciding dentofacial deformity.