Categorical Data

Types of Variables

• Categorical
• Quantitative
  • Discrete
  • Continuous

Categorical Variables

• Values that are category names or group variables
• Show frequencies or relative frequencies that observations fall into each category

Quantitative

• Numerical values for a measured or counted quantity
• Can be used for mathematical operations

Categorical data can be in numbers

Numerical data can be in categories

Discrete Variable

• A countable number of values

Continuous Variable

• Can take on infinitely many values

Discrete values can be treated as continuous if there are a lot of those values

Graphs for Categorical Data

• Pie (circle) charts- categories in relation to a whole
• Bar graphs/charts- categories in relation to each other
• Side-by-side bar graphs- bars are grouped together and placed side by side
• Segmented bar graphs- displays variable distribution as segments in a rectangle
• Mosiac plots- a three-way split of data structured like a segmented bar graph

Two-way Table

• Two categorical variables can be summarized in a two-way table
• Gives counts of observations for each combination of variables

Joint Relative Frequency

• Each cells percentage of the total (in a table)

Marginal Relative Frequency

• Focuses on only one categorical variable
• Row and column totals for a two-way table

Conditional Relative Frequency

• Relative frequency for specific row or column

Assosiation

• When one variable helps to predict the other