Quantitative or Qualitative: Overview
In introductory statistics, it’s easy to get confused between qualitative variables and quantitative variables. Quantitative means it can be counted, like “number of people per square mile.” Qualitative means it is a description, like “brown dog fur.” A Deck of cards contains quantitative variables (the numbers on the card) and qualitative variables (Spades, Hearts, Diamonds, Clubs).
The simplest way to classify Quantitative or Qualitative variables is this: if it can be added, it’s quantitative. Qualitative variables can’t be added. For example:
Cat + dog + mouse = ?
Hair color + Eye color = ?
I’m sure you could come up with a joke or two to answer those questions, but realistically you can’t add them, so they are qualitative. Technically you could add them if you assign a number to them. For example,
Cat = 1
Dog = 2
Mouse = 3
And in fact, that’s what happens a lot in statistics; Numbers are assigned to make calculations easier. But! Assigning a number does not make them a quantitative variable; They are just qualitative variables that have been assigned a number.
How to classify Quantitative or Qualitative variables
Step 1: Think of a category for the items, like “car models” or “types of potato” or “feather colors” or “numbers” or “number of widgets sold.” The name of the category is not important. Jot the category down on a piece of paper.
Step 2: Rank or order the items in your category. Some examples of items that can be ordered are: number of computers sold in a month, students’ GPAs or bank account balances. Anything with numbers or amounts can be ranked or ordered. If you find it impossible to rank or order your items, you have a qualitative item. Examples of qualitative items are “car models,” “types of potato,” “Shakespeare quotes.”
Step 3: Make sure you haven’t added information. For example, you could rank car models by popularity or expense, but popularity and expense are separate variables from “car model.” If the item is “potatoes,” it’s qualitative. If the item is “number of potatoes sold,” it’s quantitative.
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