Post-traumatic amnesia is a disorder that occurs as a direct result of a traumatic brain injury, in which the affected person is confused and unable to remember events that occurred after the injury. The person is unable to remember their condition or name, their location, or the time. New events cannot be stored in memory. About a third of patients with mild head injuries are thought to have what is called post-traumatic amnesia, in which the patient can remember only some of the events. During post-traumatic amnesia, the patient's consciousness is clouded. Post-traumatic amnesia includes confusion or disorientation in addition to the usual memory loss, so the term post-traumatic amnesia has been proposed as an alternative term. There are two types of amnesia: retrograde amnesia and anterograde amnesia. Both types may be called post-accident amnesia, or the term may be used to refer to anterograde amnesia only. Anterograde amnesia may not appear until hours after the injury, and symptoms usually improve less after loss of consciousness. A common example of head injuries in sports is a player who was able to perform the complex mental tasks of leading a football team after sustaining a concussion will have no memory of the game the next day. People with retrograde amnesia may recover partial memories later, but with anterograde amnesia memories cannot be recovered because they were not encoded accurately. The term was first used in 1928 in a paper by Simonds, who referred to the period between the injury and the return of stable and complete memory, which includes the time during which the patient was unconscious. The recovery of memories may follow a time course depending on the age of the memories, described by Ribot's law. It has been proposed as the best measure of the severity of head trauma, but may not be a reliable predictor of outcome. However, the duration of amnesia may be related to the likelihood of developing psychological and behavioral problems. Classification systems for determining the severity of brain injury may use duration of amnesia alone or in combination with other factors such as Glasgow Coma Scale scores and duration of loss of consciousness to classify brain injury into categories of mild, moderate, and severe. A common system that uses all three factors to measure the severity of brain injury and another that uses amnesia as the sole factor to determine brain injury are shown in the table to the right. The duration of amnesia usually correlates well with the Glasgow Coma Scale and lasts about four times longer than the loss of consciousness. Amnesia is considered a distinguishing feature of concussion and is used as a measure to predict the severity of concussion, for example, the Concussion Score. The concussion severity scale may be more effective than the Glasgow Coma Scale because the Glasgow Coma Scale may not be as specific. Because concussion sufferers quickly score 15—a perfect score—on the Glasgow Coma Scale, the longer the duration of amnesia or loss of consciousness immediately after the injury, indicates a longer recovery from other concussion symptoms. The longer the duration of amnesia coincides with an increased risk of complications of brain injury, such as post-traumatic epilepsy. The duration of amnesia can be difficult to measure accurately, and may be overestimated or underestimated. The Galveston Direction and Amnesia Test was designed to determine how conscious a patient is and how much material they are able to recall. The Galveston Direction and Amnesia Test is the most widely used standardized measure for assessing the likelihood of amnesia. The PTA is a 10-item test that assesses awareness and recall of events before and after the injury. It can be used to assess the duration of amnesia; this GOTA test has been found to be highly predictive of functional outcomes as measured by the Glasgow Coma Scale, with respect to productivity, psychosocial functioning, and psychological status.