Review of Prerequisites for Correlation and
Correlation is a measure of the linear relationship between two variables. The Pearson Product Moment Correlation Coefficient, represented by r, ranges from +1.00 for a perfect positive relationship to -1.00 for a perfect negative relationship. If there is no linear relationship, r=0. Thus, r indicates both the direction (positive or negative) and the strength of the linear relationship (e.g., weak or strong).
If a relationship is nonlinear, then simple r and regression may not be the appropriate model.
Example and review questions. A professor is interested in the relationship between attendance and exam grades. The professor gives an exam during the fifth week of class. In addition to the exam grade, the professor also records the number of class sessions attended by each student (12 possible).The graph below summarizes the relationship.
Question 1: How would you describe this relationship?
A. More attendance is associated with higher grades, less attendance is associated with lower grades.
B. Less attendance is associated with better grades, more attendance is associated with worse grades.
C. Attendance isn't related to grades.