Categorical Variables

Statistics

The science and art of collecting, analyzing, and drawing conclusions from data.

Individual

An object described in a set of data. Individuals can be people, animals, or things.

Variable

An attribute that can take different values for different individuals.

Categorical variable

Assigns labels that place each individual into a particular group, called a category.

Quantitative variable

Takes number values that are quantities—counts or measurements.

Discrete variable

A quantitative variable that takes a fixed set of possible values with gaps between them.

continuous variable

A quantitative variable that can take any value in an interval on the number line.

Distribution

Of a variable, tells us what values the variable takes and how often it takes those values.

Frequency table

Shows the number of individuals having each value.

Relative frequency table

Shows the proportion or percent of individuals having each value.

Bar graph

Shows each category as a bar. The heights of the bars show the category frequencies or relative frequencies.

Pie chart

Shows each category as a slice of the "pie." The areas of the slices are proportional to the category frequencies or relative frequencies.

Two-way table

A table of counts that summarizes data on the relationship between two categorical variables for some group of individuals.

Marginal relative frequency

Gives the percent or proportion of individuals that have a specific value for one categorical variable.

Joint relative frequency

Gives the percent or proportion of individuals that have a specific value for one categorical variable and a specific value for another categorical variable.

Conditional relative frequency

Gives the percent or proportion of individuals that have a specific value for one categorical variable among individuals who share the same value of another categorical variable (the condition).

Side-by-side bar graph

Displays the distribution of a categorical variable for each value of another categorical variable. The bars are grouped together based on the values of one of the categorical variables and placed side by side.

Segmented bar graph

Displays the distribution of a categorical variable as segments of a rectangle, with the area of each segment proportional to the percent of individuals in the corresponding category.