Restoring self-control when intoxicated. Refer to the Experimental and Clinical Psychopharmacology (February 2005) study of self-control when intoxicated, presented in Exercise 10.34 (p. 495). After memorizing two lists of words (20 words on a green list and 20 words on a red list), students were randomly assigned to one of four different treatment groups. Students in Group A received two alcoholic drinks. Students in Group AC had caffeine powder dissolved in their alcoholic drinks. Group AR also received two alcoholic drinks, but received a monetary award for correct responses. Students in Group P (the placebo group) were told that they would receive alcohol, but instead received two drinks containing a carbonated beverage (with a few drops of alcohol on the surface to provide an alcoholic scent). After consuming their drinks and resting for 25 minutes, the students performed a word completion task. Their scores (simulated on the basis of summary information from the article) are reported in the accompanying table and saved in the DRINKERS file. (Note: A score represents the difference between the proportion of correct responses on the green list of words and the proportion of incorrect responses on the red list of words.) Compare the task score distributions of the four groups, using an appropriate nonparametric test at a = .05. What can you infer about the four groups of students?

Exercise 10.34

Restoring self-control when intoxicated. Does coffee or some other form of stimulation (e.g., an incentive to stop when seeing a flashing red light on a car) really allow a person suffering from alcohol intoxication to “sober up”? Psychologists from the University of Waterloo investigated the matter in Experimental and Clinical Psychopharmacology (February 2005). A sample of 44 healthy male college students participated in the experiment. Each student was asked to memorize a list of 40 words (20 words on a green list and 20 words on a red list). The students were then randomly assigned to one of four different treatment groups (11 students in each group). Students in three of the groups were each given two alcoholic beverages to drink prior to performing a word completion task. Students in Group A received only the alcoholic drinks. Participants in Group AC had caffeine powder dissolved in their drinks. Group AR participants received a monetary award for correct responses on the word completion task. Students in Group P (the placebo group) were told that they would receive alcohol, but instead received two drinks containing a carbonated beverage (with a few drops of alcohol on the surface to provide an alcoholic scent). After consuming their drinks and resting for 25 minutes, the students performed the word completion task. Their scores (simulated on the basis of summary information from

article) are reported in the table on the previous page and saved in the DRINKERS file. (Note: A task score represents the difference between the proportion of correct responses on the green list of words and the proportion of incorrect responses on the red list of words.)

a. What type of experimental design is employed in this study?

b. Analyze the data for the researchers, using a = .05. Are there differences among the mean task scores for the four groups?

c. What assumptions must be met in order to ensure the validity of the inference you made in part b?