Types of Variables - Categorical

Categorical Variables

As the name implies, a categorical variable is made up of categories. Typically, there are a set number of categories a participant can select from and each category is distinct from the other. Familiar types of categorical variables are variables like ethnicity or marital status. A unique characteristic of many categorical variables (especially binary and nominal) is that the categories are not necessarily ordered in a meaningful way. A variable for ethnicity may be coded the following way:  African American as 1, Asian as 2, and Caucasian as 3. Which ethnicity gets assigned which number is arbitrary, so the numerical ordering of the variable doesn’t provide information about ethnicity.

A simple version of a categorical variable is called a binary variable. This type of variable lists two distinct, mutually exclusive choices. One example of a binary variable is gender (i.e., male or female).

Binary Variable Example
 

I am a:
         Male
         Female

 

A categorical variable that has more than two categories to select from is called a nominal variable.

Nominal Variable Example
 

How do you describe yourself? (select all that apply)

  • African American, not of Hispanic origin
  • American Indian or Alaskan Native
  • Asian/Pacific Islander
  • Hispanic/Latino
  • White, not of Hispanic origin
  • Other, please specify ______________ 

 

Another version of a categorical variable is an ordinal variable, a variable with categories that can be put in a logical order. However, ordinal data do not tell us about the differences between the categories. The differences between the categories could be unknown or inconsistent. For example, a participant might be asked to describe their income as low, medium, or high. While these categories can be ordered in a logical way, there is no determined increment between each.  We know that high is more than medium, but we don’t know by how much. 

Ordinal Variable Example

 

What is your highest level of education completed?

  • Less than high school
  • High school diploma/GED
  • Some college
  • Associate's degree
  • Bachelor's degree
  • Graduate degree

 


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