Head trauma study. The SCL-90-R is a 90-item symptom inventory checklist designed to refle...

Head trauma study. The SCL-90-R is a 90-item symptom inventory checklist designed to reflect the psychological status of an individual. Each symptom (e.g., obsessive-compulsive behavior) is scored on a scale of 0 (none) to 4 (extreme). The total of these scores yields an individual’s Positive Symptom Total (PST). “Normal” individuals are known to have a mean PST of about 40. The Journal of Head Trauma Rehabilitation (April 1995) reported that a sample of 23 patients diagnosed with mild to moderate traumatic brain injury had a mean PST score of  and a standard deviation of s = 20.76. Is there sufficient evidence to claim that the true mean PST score of all patients with mild-to-moderate traumatic brain injury exceeds the “normal” value of 40? Test, using α = .05.