# Scatter Diagram

Scatter diagrams are used to study possible relationships between two variables. Although these diagrams cannot prove that one variable causes the other, they do indicate the existence of a relationship, as well as the strength of that relationship. It is composed of a horizontal axis containing the measured values of one variable and a vertical axis representing the measurements of the other variable.

The purpose of the scatter diagram is to display what happens to one variable when another variable is changed. The diagram is used to test a theory that the two variables are related. The type of relationship that exists is indicated by the slope of the diagram. The scatter diagram shows the pattern of relationship between two variables that are thought to be related.

For example, is there a relationship between out side temperature and cases of the common cold? As temperatures drop, do colds increase? The closer the points hug a diagonal line the more closely there is a one to one relationship. The statistical test to use to test the strength of the relationship is Pearson's r.