Naming a variable

The name of a variable is like the last name of a family because it applies to all family members who are distinguishable by their first names.

Example 1:
The family of "gender" has two members, "male" gender and "female" gender.

Example 2:
The Likert scale family of "degree of agreement" has five members: "Strongly disagree", "disagree", "neutral", "agree", and "strongly agree."

Example 3:
The family of "SAT score" has many many possible members who are represented by specific test scores.

But sometimes it's not very obvious what the "last name" of the variable family is. For example, if we want to see if retaining a child in a grade enables her to make more progress at the end of a year, we may compare "children retained in a grade" with "children with the same level of test scores but promoted to the next grade anyway". What would be the variable to represent the two conditions of retention and no-retention?

Here's another example. We would like to see if playing violent video games affects children's playground behavior, we might compare behavior of "kids playing violent games" and "those playing non-violent video games". What would be the variable name to capture these two types of video games?

To name the variable (family), we want a label that is neutral so that each family member (variable level) can fit the label. For the grade retention example, we can name the variable "grade retention" or "grade retention status", and the two groups of kids vary along this factor. For the video game example, we can name the variable "violence in video game" so that one group experience the presence of violence but the other group experience the absence of violence in video games.

If you think of variable and their specific levels or values as family and family members, you can avoid the common mistake of describing the specific levels or values as "variables," such as the error of calling violent games and non-violent games as two variables when they belong to the same variable (family).