This document defines correlation as the relationship between two variables and how they depart from independence. It provides examples of correlational research questions about the relationship between time spent on homework and grades or junk food in schools and obesity. While correlation suggests an association, it does not prove that one variable causes the other. The example of past beliefs about ulcers being caused by stress and spicy foods is given, but researchers now know ulcers are actually caused by H. pylori bacteria. Correlation research can help design better experimental studies to understand causation.