Correlation test is used to evaluate the association between two or more variables. Scatter diagram is a graph in which the values of two variables are plotted along two axes, the pattern of the resulting points revealing any correlation present. Frequency distribution is a mathematical function showing the number of instances in which a variable takes each of its possible values. A two-way table (also called a contingency table) is a useful tool for examining relationships between categorical variables. The entries in the cells of a two-way table can be frequency counts or relative frequencies. A rank correlation is any of several statistics that measure an ordinal association—the relationship between rankings of different ordinal variables or different rankings of the same variable. A rank correlation coefficient measures the degree of similarity between two rankings, and can be used to assess the significance of the relation between them.