In a study examining the effect of alcohol on reaction time, Liguori and Robinson (2001) found that even moderate alcohol consumption significantly slowed response time to an emergency situation in a driving simulation. In a similar study, researchers measured reaction time 30 minutes after participants consumed one 6-ounce glass of wine. Again, they used a standardized driving simulation task for which the regular population averages = 400 msec. The distribution is approximately normal with _x = 45. Assume that the researcher obtained a sample mean of M = 422 for the n = 25 participants in the study.

a. Are the data sufficient to conclude that the alcohol has a significant effect on reaction time? Use a two-tailed test with = 0.01.

b. Do the data provide evidence that the alcohol significantly increased (slowed) reaction time? Use a one-tailed test with = 0.01.

c. Compute Cohen's d for the effect size.

d. Explain why your answers in a and b differed.