Functions can be used to model real-world events and interpret data from those events. Data that measures or compares two characteristics of a population is known as bivariate data.

When analyzing and interpreting data, we often look for a relationship between two variables called an association. We can describe an association according to the form, direction, or strength of the relationship between the two variables.

For numerical data, descriptions include:

• linear or nonlinear
• positive or negative
• strong or weak

For categorical data, descriptions include:

• strong or weak

To more easily analyse a set of data and determine if there is an association between the variables, we often construct a graph of the data, known as a scatter plot. On a scatter plot, we can then draw a line that best estimates the relationship between two sets of data, called a line of fit or trend line.

Worked examples