A study of the effects of the relationship among caffeine consumption, introversion/extraversion, and trait anxiety on performance

Abstract

The purpose of this study was to examine the effects of the relationship among caffeine consumption, levels of trait anxiety, and the personality factor of introversion/ extraversion on performance. In Phase I of this study, volunteers were screened for introversion/extraversi on using the Eysenck Personality Inventory (EPI) and fhigh/low trait anxiety using the State-Trait Anxiety Inventory (STAI). Based on the results of the two screening instruments the volunteers were categorized as high trait-anxious introverts (HTA/I), low trait-anxious introverts (LTA/I), high trait-anxious extraverts (HTA/E), or low trait-anxious extraverts (LTA/E). Using a table of random numbers, 30 subjects from each category were selected. These subjects were further randomly assigned to one of the two treatment levels of caffeine.In Phase II of this study each of the 120 subjects consumed either two milligrams of caffeine per kilogram of body weight or four milligrams of caffeine per kilogram of body weight in six ounces of Tang. After a 45-minute waiting period for the caffeine to enter the blood system, each subject completed the performance task, a seven-minute modified version of the Digit Symbol Scale (DSS) of the Wechsler Adult Intelliqence Scale (WAIS). The dependent variable was the total number of correct responses out of a possible score of 490.The hypotheses were tested using a Three-Way Analysis of Variance, and the F-test was applied to determine statistical significance. None of the three null hypotheses were rejected.