Question

2. In a study examining the effect of caffeine on reaction time, Liguori and Robinson (2001) measured reaction time 30 minutes after participants consumed one 6-ounce cup of coffee and they used standardized driving simulation task for which the regular population averages μ = 415 msec. The distribution of reaction times is approximately normal with σ = 40. Assume that the researcher obtained a sample mean of M = 400 msec for the n = 36 participants in the study. Can the researcher conclude that caffeine has a significant effect on reaction time? Use a two-tailed test (i.e., non-directional) with α = .05.

a. State the null hypothesis in words and in a statistical form

b. State the alternative hypothesis in words and a statistical form.

c. Compute the appropriate statistic to test the hypotheses. Sketch the distribution with the standard error and locate the critical region with the critical value. Use α = .05

d. State your statistical decision.

e. What is your conclusion? (don't forget the statistical information).

f. Given your statistical decision (in part d), what type of decision error could you have

made and what is the probability of making that error?

g. Compute Cohen’s d to measure the size of the effect. Interpret what this effect size really means in this context (don’t just say “large effect” or “small effect”).

h. In the above question, if you changed the alpha level from .05 to .01, would that

have affected your statistical decision? If so, explain your answer.

i. If the alpha level is changed from .05 to .01, what happens to the boundaries for the critical region?

j. If the alpha level is changed from .05 to .01, what happens to the probability of a Type I error?

Answer 1