Anxiety disorders and symptoms can often be effectively treated with benzodiazepine medications. It is known that animals exposed to stress exhibit a decrease in benzodiazepine receptor binding in the frontal cortex. The paper “Decreased Benzodiazepine Receptor Binding in Prefrontal Cortex in Combat-Related Posttraumatic Stress Disorder” (Amer. J. of Psychiatry, 2000: 1120–1126) described the first study of benzodiazepine receptor binding in individuals suffering from PTSD. The accompanying data on a receptor binding measure (adjusted distribution volume) was read from a graph in the paper. PTSD: 10, 20, 25, 28, 31, 35, 37, 38, 38, 39, 39, 42, 46 Healthy: 23, 39, 40, 41, 43, 47, 51, 58, 63, 66, 67, 69, 72

a. Is it plausible that the population distributions from which these samples were selected are normal?

b. Calculate an interval for which you can be 95% confident that at least 95% of all healthy individuals in the population have adjusted distribution volumes lying between the limits of the interval.

c. Predict the adjusted distribution volume of a single healthy individual by calculating a 95% prediction interval. How does this interval’s width compare to the width of the interval calculated in part (b)?

d. Estimate the difference between the true average measures in a way that conveys information about reliability and precision.