Which is the best prognostic factor in a case of head injury?

The best prognostic factor for head injury is glasgow coma scale. The GCS is determined by adding the scores of the best responses of the patient in each of three categories such as eye opening, best motor response and verbal response. Maximum score is 15 and minimum score is 3. Traumatic brain injury is classified according to GCS score as mild (score 14-15), moderate (scores 9-13) and severe (scores 3-8). Over 85% of patients with scores of 3 or 4 die within 24 hrs. Ref: Harrison's Principles Of Internal Medicine, 16th Edition, page 2450,2451 ; Anaesthesia, Pharmacology, Intensive Care and Emergency Volume 23 By Antonino Gullo, page 305