Cocaine is thought to affect the brain by blocking the dopamine transporter, increasing the amount of dopamine in the nerve synapse. To investigate this idea, Volkow et al. (1997) administered intravenous doses of 0.3 to 0.6 mg/kg of cocaine to volunteers. They used PET scans to compare the magnitude of the perceived “high” of regular cocaine users with the percentage of dopamine receptors blocked. The results for 34 subjects are illustrated below. Full data are available at whitlockschluter3e.zoology.ubc.ca.

a. Using the following quantities, calculated from these data, estimate the correlation between the percentage of dopamine receptors blocked and subjects’ ratings of the cocaine high. Provide a standard error with your estimate.

b. Calculate a 99% confidence interval for the correlation in the population.

c. What are your assumptions in part (b)?

d. Imagine the following scenario: A second team of researchers carried out a similar study using the same population and sample size. They used a narrower range of intravenous doses of cocaine in their experiment, which led to a smaller range of values than in the first study for the percentage of dopamine receptors blocked. When they analyzed their results, they found only a low correlation between percentage dopamine receptors blocked and perceived high. In their published report, they concluded that the true correlation between these variables is much lower than estimated in the Volkow et al. study. Who is right? Explain.

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Rating of high 10- 8- 2 0 30 ● 40 50 60 70 80 90 Dopamine transporters blocked (%)