What does it mean to have a CI with positive and negative values? At a university, there are typically four distinctions based on seniority; that is, how long you've been a student: freshman, sophomore, junior, or senior. A student might be satisfied or dissatisfied with their university experience, and that answer might change as a student progresses through the levels of seniority. Suppose that we calculate a 95% confidence interval for the difference in the population proportion of freshmen who are satisfied with their university experience (1) and the population proportion of seniors who are satisfied with their university experience (2), and find that interval to be (-0.01, 0.04).