Some questions, such as "What is your height?," are answered with a number. Answers to questions like "What is your sex?" do not require a number.
We distinguish between variables that are measured in numbers and those that are not. This distinction becomes useful and important when we get to the analysis phase of statistical problem solving. These two types of variables are called quantitative variables and qualitative variables.
Quantitative variables represent numbers or quantities; in fact, they are sometimes referred to as numerical variables. A test score, the number of votes cast in an election, the measured amount of soda in a two-liter bottle -- these are all examples of quantitative variables.
Rather than numbers, qualitative variables represent categories, such as "excellent" or "female," and they are sometimes referred to as categorical variables. The hometown of a college student, the favorite TV show of a politician, and the model of a car seen on a highway -- these are all qualitative variables.
We refer to data in the same terms.
Data are called quantitative if they come from measurements of a quantitative variable.
Data are called qualitative if they come from measurements of a qualitative variable.