MA

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