Brain Volume and Psychiatric Disorders A 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 (in mL) are given below for total brain volumes (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).

a. Construct a 95% confidence interval for the difference between the mean brain volume of obsessive-compulsive patients and the mean brain volume of healthy persons. Assume that the two populations have unequal variances.

b. Assuming that the population variances are unequal, use a 0.05 significance level to test the claim that there is no difference between the mean for obsessivecompulsive patients and the mean for healthy persons.

c. Based on the results from parts

(a) and (b), does it appear that the total brain volume can be used as an indicator of obsessive-compulsive disorders?

Obsessive-compulsive patients: n 5 10, 5 1390.03, s 5 156.84 Control group: n 5 10, x 5 1268.41, s 5 137.97