1.1.1 - Categorical & Quantitative Variables
Variables can be classified as categorical or quantitative. Categorical variables are those that provide groupings that may have no logical order, or a logical order with inconsistent differences between groups (e.g., the difference between 1st place and 2 second place in a race is not equivalent to the difference between 3rd place and 4th place). Quantitative variables have numerical values with consistent intervals.
- Categorical variable
- Names or labels (i.e., categories) with no logical order or with a logical order but inconsistent differences between groups (e.g., rankings), also known as qualitative.
- Quantitative variable
- Numerical values with magnitudes that can be placed in a meaningful order with consistent intervals, also known as numerical.
Example: Weight Section
A team of medical researchers weigh participants in kilograms. Weight in kilograms is a quantitative variable because it takes on numerical values with meaningful magnitudes and equal intervals.
Example: Favorite Ice Cream Flavor Section
A teacher conducts a poll in her class. She asks her students if they would prefer chocolate, vanilla, or strawberry ice cream at their class party. Preferred ice cream flavor is a categorical variable because the different flavors are categories with no meaningful order of magnitudes.
Example: Birth Location Section
A survey asks “On which continent were you born?” This is a categorical variable because the different continents represent categories without a meaningful order of magnitudes.
Example: Children per Household Section
A census asks every household in a city how many children under the age of 18 reside there. Number of children in a household is a quantitative variable because it has a numerical value with a meaningful order and equal intervals.
Example: Highway Mile Markers Section
When a car breaks down on the highway, the emergency dispatcher may ask for the nearest mile marker. Highway mile marker value is a quantitative variable because it is numeric with a meaningful order of magnitudes and equal intervals.
Example: Running Distance Section
A runner records the distance he runs each day in miles. Distance in miles is a quantitative variable because it takes on numerical values with meaningful magnitudes and equal intervals.
Example: Highest Level of Education Section
A census asks residents for the highest level of education they have obtained: less than high school, high school, 2-year degree, 4-year degree, master's degree, doctoral/professional degree. This is a categorical variable. While there is a meaningful order of educational attainment, the differences between each category are not consistent. For example, the difference between high school and 2-year degree is not the same as the difference between a master's degree and a doctoral/professional degree. Because there are not equal intervals, this variable cannot be classified as quantitative.
Example: Online Courses Taught Section
A survey designed for online instructors asks, "How many online courses have you taught?" Three options are given: "none," "some," or "many." While there is a meaningful order of magnitudes, there are not equal intervals. This is a categorical variable.
If the survey had asked, "How many online courses have you taught? Enter a number." this would be a quantitative variable. Here, participants are answering with the number of online courses they have taught. This is a numerical value with a meaningful order of magnitudes and equal intervals.