Uses of Correlation and Regression

RELATIONSHIPS BETWEEN TWO VARIABLES

In Figure 12.1, we present examples of several types of relationships between two variables. Note that the horizontal and vertical axes are denoted by the symbols X and Y, respectively.

Both Figures 12.1A and 12.1B represent linear associations, whereas the remaining figures illustrate nonlinear associations. Figures 12.1A and 12.1B portray direct and inverse linear associations, respectively. The remaining figures represent non-linear associations, which cannot be assessed directly by using a Pearson correlation coefficient. To assess these types of associations, we will need to apply other statistical methods such as those described in Chapter 14 (nonparametric tests). In other cases, we can use data transformations, a topic that will be discussed briefly later in this text.