ABSTRACT

Introduction Researchers are often interested in the relationship between two, or more, variables. For example, they may want to know how the variable IQ is related to the variable earnings.

The chapter starts by explaining the measures, including correlation, that are used to quantify the relationship between variables and how to interpret those measures. It discusses the basic forms of correlation for different types of data. It then introduces extensions of these techniques and the use of correlation for investigating the reliability and validity of measures.