is there evidence that chocolate improves your mood? a sample of 35 college students volunteered for this study. during the first phase of the study, the 35 subjects completed a mood survey (range values 0-very bad mood to 10-extremely good mood) at the end of a week in which they did not consume chocolate. during the second phase, the 35 subjects ate chocolate at noon every day for a week. at the end of that week, the 35 subjects completed a mood survey. researchers calculated the difference between survey's values at the end of the second phase and at the end of the first phase of the study. the appropriate test to answer this question is: