Correlation and Linear Regression
Oftentimes, when conducting a study or an experiment, a researcher is interested in knowing whether or not an association between two quantitative variables exists. For example, do people who retire earlier tend to live longer than those who work until an older age? Is there an association between a female’s annual salary and her education level? Is the amount of minutes per day that a person spends on Facebook associated with the number of friends that he has? In this chapter we investigate quantitative bivariate data.
Bivariate data are data that have been collected by measuring two variables on each individual. Our goal will be to see if an association exists between a pair of variables, and if one does exists, to describe the association.
In this chapter we focus on looking at bivariate quantitative data. We begin by graphing bivariate quantitative data and determining the level and type of association (if any) that exists between the two variables. If the “right” kind of association between the two variables does exist, we’ll see later in this chapter how to find a model to represent the relationship.