Pearson's Correlation Coefficient:

• Tells you if there is a linear relationship between two variables.
  
  
• Tells you how good the relationship is by seeing if r is close to 1 or -1 or r² is close to 1.0.
  
  
• Tells you if the relationship is positive or negative by whether r is positive or negative.
  
  
• Can be used to calculate a straight line so you can predict one score from another.

Every time you take a standardized test - someone is doing this to you. The "r" is out there!