CASE STUDY Is caffeine dependence real? Researchers at the Johns Hopkins University School of Medicine wanted to determine if some individuals develop a serious addiction called caffeine dependence syndrome. Eleven volunteers were recruited who were diagnosed as caffeine dependent. For a two-day period, these volunteers were given a capsule that either contained their daily amount of caffeine or a fake (nonactive) substance. Over another two-day period, at least one week after the first, the contents of the capsules received were switched. Whether the subjects first received the capsule containing caffeine or the capsule with the fake substance was determined by randomization. The subjects’ diets were restricted during the study periods. All products with caffeine were prohibited, but to divert the subjects’ attention from caffeine, products containing ingredients such as artificial sweeteners were also prohibited. Questionnaires assessing depression, mood, and the presence of certain physical symptoms were administered at the end of each two-day period. The subjects also completed a tapping task in which they were instructed to press a button 200 times as fast as they could. Finally, subjects were interviewed by a researcher, who did not know what was in the capsules the subjects had taken, to find other evidence of functional impairment. The Electronic Encyclopedia of Statistical Examples and Exercises (EESEE) story “Is Caffeine Dependence Real?” contains more information about this study. EESEE stories are available in LaunchPad.

Is this a good study? By the end of this chapter, you will be able to determine the strengths and weaknesses of a study such as this.