The researchers in the previous problem also examined the effect of caffeine on response time in the driving simulator. In a similar study, researchers measured reaction time 30 minutes after participants consumed one 6-ounce cup of coffee. Using the same driving simulation task, for with the distribution of reaction times is normal with = 400 msec and _x = 40, they obtained a mean of M = 392 for a sample of n = 36 participants.

a. Would you use a one-tailed or a two-tailed test for this question? Briefly explain your reasoning.

b. Carry out a hypothesis test using the test you identified in a with = 0.05. Make a conclusion and, if appropriate, calculate and interpret Cohen's d.