CLASSIFICATION OF VARIABLES

Variable:
A characteristic that varies from one person or thing to another is called a variable. Examples of variables for humans are height, weight, number of siblings, sex, marital status, and eye color.

Numerical or Quantitative Variables:

A numerically valued variable is called quantitative variable. Height, weight and number of siblings yield numerical information and are examples of quantitative variable.

Numerical variables include both discrete and continuous variables. A discrete numerical variable produces a response that comes from a counting process.
•    A professor is asked the number of students that are enrolled in a class;
•    A student is asked how many times a week an assignment is completed in the in the in the computer lab;
•    An investor is asked how stocks of Microsoft are in investor’s portfolio;
•    An insurance company wants to know how many claims were filled following a hurricane.

Responses to each these questions are 0, 1, 2, and so forth.

A continuous numerical variable produces a response that is the outcome of a measurement process. For example, you might tell someone, that you are 6 feet (or 72 inches) tall, but your height could actually be 72.1 inches or 71.8 inches, or some other similar numbers depending on the accuracy of the instrument used to measure your height. You might state your age “20 years,” but you are constantly aging. You are actually 20 years, 3 months, 2 days, 5 hours, 4 minutes, 12 (now it’s 13) second old. Sounds absurd. So you just say 20 years. The actual weight of packages could also deviate within a certain amount depending on the precision of the instrument used to weight each package.  
 

Categorical or Qualitative Variables: 

A non-numerically valued variable is called qualitative variable. Sex, marital status, and eye color yield non-numerical information and are examples of qualitative variables.

Categorical variables produce responses that belong to groups (sometimes called “classes”) or categories. For example, responses to yes/no type questions belong in this category. “Do you own a cellular phone” or “Do you have any homework tonight” or “Have you ever been in London” are limited to yes or no answers. A health care insurance company may ask if a claim was incorrectly processed. The operations manager at a water bottling company asks if bottles are properly filled. Sometimes, categorical variables include a range of choices such as “strongly disagree” to “strongly agree”.