of people who have a head injury with symptoms of concussion and no radiological evidence of brain lesions meet these criteria. In addition to these symptoms, people that meet the ICD-10 criteria for PCS may fear that they will have permanent brain damage, which may worsen the original symptoms. Preoccupation with the injury may be accompanied by the assumption of a "sick role" and hypochondriasis. The criteria focus on subjective symptoms and mention that neuropsychological evidence of significant impairment is not present. With their focus on psychological factors, the ICD-10 criteria support the idea that the cause of PCS is functional. Like the ICD-10, the ICD-9-CM defines PCS in terms of subjective symptoms and discusses the greater frequency of PCS in people with histories of mental disorders or a financial incentive for a diagnosis. The DSM-IV lists criteria for diagnosis of PCD in people who have had a head trauma with persistent post-traumatic amnesia, loss of consciousness, or post-traumatic seizures. In addition, for a diagnosis of PCD, patients must have neuropsychological impairment as well as at least three of the symptoms marked with a check mark in the table at right under "DSM-IV". These symptoms must be present for three months after the injury and must have been absent or less severe before the injury. In addition, the patient must experience social problems as a result, and must not meet criteria for another disorder that explains the symptoms better. Neuropsychological tests exist to measure deficits in cognitive functioning that can result from PCS. The Stroop Color Test and the 2&7 Processing Speed Test (which both detect deficits in speed of mental processing) can predict the development of cognitive problems from PCS. A test called the Rivermead Postconcussion Symptoms Questionnaire, a set of questions that measure the severity of 16 different post-concussion symptoms, can be self-administered or administered by an interviewer. Other tests that can predict the development of PCS include the Hopkins Verbal Learning A test (HVLA) and the Digit Span Forward examination. The HVLA tests verbal learning and memory by presenting a series of words and assigning points based on the number recalled, and digit span measures attention efficiency by asking the examinee to repeat back digits spoken by the tester in the same order as they are presented. In addition, neuropsychological tests may be performed to detect malingering (exaggerating or making up symptoms) . Differential diagnosis PCS, which