When considering the use of the initial GCS for prognosis, the two most important problems are the reliability of the initial measurement, and its lack of precision for prediction of a good outcome if the initial GCS is low. If the initial GCS is reliably obtained and not tainted by prehospital medications or intubation, approximately 20% of the patients with the worst initial GCS will survive and 8-10% will have a functional survival (GOS 4-5).