A value close to -1 indicates a negative linear correlation; that is, when one variable increases the other decreases. A value close to 0 indicates a non-linear, or random, correlation. The equation for calculating the correlation coefficient is where Xi and Yi are the set of variables, and the sample means.
A demographic is a subset of a population that shares a common factor such as age, income or education level. The Millennial generation, for example, is the demographic cohort that immediately follows Generation X. Although there is a great deal of variation from one individual to another within any generational cohort, the particular environment for any generation affects those individuals in ways that are observable as broad tendencies.
Demographic data is also vital in the education process, as it allows students and teachers to gather a clearer understanding of who makes up the United States, and how their lifestyles have changed and evolved over the years.