**What Are Variables?**

A **subject** is a person, place, or thing we’re interested in studying.

A **variable** is an attribute that describes the subject in some way.

Variables can vary from subject to subject.

For example, recall our dataset about basketball player heights from the previous section:

The subjects are the athletes. The **variable** we are interested in is height. Notice how it varies from player to player.

As another example, recall our dataset about city populations also from the previous section:

The subjects are the cities. The variable we are interested in is population. Notice how it varies from city to city.

**Quantitative vs. Qualitative Variables**

Variables can be classified as **quantitative** (sometimes called “numerical”) or **qualitative** (sometimes called “categorical).

**Quantitative variables** describe a *quantity* about a subject. They are numeric. For example, the population of a city is a quantitative variable. So is the height of basketball players. Both of these variables measure a numeric quantity.

**Qualitative variables** describe a *quality* about a subject. They can take on names, labels, or categories. For example, the color of hair (“blonde”, “brunette”, “grey”) or the type of a car (“SUV”, “minivan”, “sports car”) are both qualitative variables.

**Continuous vs. Discrete Variables**

Quantitative variables can be further classified as **discrete** or **continuous**.

**Discrete:** Discrete variables can only have certain values. For example:

- The number of students in a class – it could be 20 students, but it couldn’t be 20.2 students or 20.223 students.

- The number of cars in a parking lot – there could be 100 cars, but there couldn’t be 100.5 cars or 100.38 cars.

**Continuous:** Continuous variables can take on an infinite number of values. For example:

- body weight – you could weigh 180.332 pounds. Or you could weigh 190.5 pounds. Body weight can take on
*any*value.

- temperature – it could be 65.55 degrees Fahrenheit outside. Or it could be 45.998 degrees Fahrenheit outside. Temperature can take on
*any*value.

Rule of Thumb: If you are *counting* something, it is discrete data. (“Count the number of gummy bears in the bag”). But if you are *measuring* something, it is continuous data (Measuring weight, height, speed, etc.)