When working with statistics, it's important to understand some of the terminology used, including quantitative and categorical variables and how they differ. The trick is to get a handle on the lingo right from the get-go, so when it comes time to work the problems, you’ll pick up on cues from the wording and get going in the right direction.
Quantitative variables
Quantitative variables are measured and expressed numerically, have numeric meaning, and can be used in calculations. (That’s why another name for them is numerical variables.) Although zip codes are written in numbers, the numbers are simply convenient labels and don’t have numeric meaning (for example, you wouldn’t add together two zip codes).
Categorical variables
A categorical variable doesn’t have numerical or quantitative meaning but simply describes a quality or characteristic of something.
The numbers used in categorical or qualitative data designate a quality rather than a measurement or quantity. For example, you can assign the number 1 to a person who’s married and the number 2 to a person who isn’t married. The numbers themselves don’t have meaning — that is, you wouldn’t add the numbers together.
Sample questions
Which of the following is an example of a quantitative variable (also known as a numerical variable)?
(A) the color of an automobile
(B) a person’s state of residence
(C) a person’s zip code
(D) a person’s height, recorded in inches
(E) Choices (C) and (D)
Answer: D. a person’s height, recorded in inches
Which of the following is an example of a categorical variable (also known as a qualitative variable)?
(A) years of schooling completed
(B) college major
(C) high-school graduate or not
(D) annual income (in dollars)
(E) Choices (B) and (C)
Answer: E. Choices (B) and (C) (college major; high-school graduate or not)
College major (such as English or mathematics) and high-school graduate (yes or no) both describe non-numerical qualities.
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