Hypothesis Test for Identifying Psychiatric Disorders Are severe psychiatric disorders related to biological factors that can be physically observed? One study used x-ray computed tomography (CT) to collect data on brain volumes for a group of patients with obsessive-compulsive disorders and a control group of healthy persons.

Sample results for volumes (in mL) follow for the right cordate (based on data from

“Neuroanatomical Abnormalities in Obsessive-Compulsive Disorder Detected with Quantitative X-Ray Computed Tomography,” by Luxenberg et al., American Journal of Psychiatry, Vol. 145, No. 9). Construct a 99% confidence interval estimate of the difference between the mean brain volume for the healthy control group and the mean brain volume for the obsessive-compulsive group. What does the confidence interval suggest about the difference between the two population means? Based on this result, does it seem that obsessive-compulsive disorders have a biological basis?

Control group: n 5 10, 5 0.45, s 5 0.08 Obsessive-compulsive patients: n 5 10, 5 0.34, s 5 0.08