Which of the following is an example of a categorical variable?

A categorical variable is one that represents distinct categories or groups and typically does not have a numerical value associated with it. In the provided options, gender is clearly an example of a categorical variable, as it consists of categories such as male, female, or non-binary. These categories are qualitative and cannot be mathematically quantified in the same way that numerical data like income, age, or height can be.

Income, age, and height are all examples of quantitative variables because they can be expressed numerically and measure a magnitude or amount. For instance, income can be measured in dollars, age in years, and height in centimeters or inches. These types of variables allow for mathematical operations, unlike categorical variables, which focus on grouping data without inherent numerical value. Thus, recognizing gender as a categorical variable is key in understanding how different types of data can be classified in statistical analysis.