Types of Variables

What are the Types of Variables?

Variable refers to a characteristics or phenomena that changes or varies over time for different individual or objects under consideration (Mendenhall, et.al., 2012).

Data

Data are the values that the variables can assume (Reston, 2004).

Experimental unit

Experimental unit is the individual or object on which a variable is measured.

Types of variable according to a functional relationship

Independent variable. This is sometimes termed as a predictor variable if the object is to predict the value of one variable on the basis of the other.

Dependent variable. This is sometimes called the criterion variable and whose value is predicted. For example, academic achievement is dependent on Intelligent Quotient, study habits, interests, attitudes and many more. Hence, IQ, study habits, interests, attitudes are independent variables. On the other hand, academic achievement is the dependent variable.

Types of variable according to the attribute of objects they classify

         Qualitative Variables. These are words or codes that represent a class or category. Further, produce data that can be categorized according to similarities or differences in kind. Also known as a categorical variable. 

Here are some examples: gender, taste ranking, religious affiliation, academic achievement, marital status, type of high school attended and many more.

Quantitative Variables. These are variables that classify objects or represent an amount or a count. This is a variable often represented by an arbitrary letter, let say x, produce numerical data. 

Here are some examples: Height, student enrolment, class size, family size, test scores, entrance test results, crime rate, salary, number of passengers, a volume of orange juice, etc.

Types of variable according to the continuity of values

Discrete variable. This refers to variables that can be obtained, can assume only a finite or through a countable number of values.

Examples are: Number of family members, number of new car sales, number of defective bulbs, faculty size, hospital staff size, number of students enrolled in Statistics course, number of bedrooms in a house, etc.

Continuous variable. Variables that can assume many values corresponding to the points on a line interval. 

Here are some examples: Crime rates, cell density, rainfall, temperature, air pressure, weight, height, study hours, time, salary, distance traveled, etc. 

Types of variable according to the Scale of Measurements

Nominal scale is often referred to as a categorical scale. This only satisfies the identity property of measurement. 

For example, gender, Religion, and political affiliation.

Ordinal scale has an ordered relationship to every other value on the scale. 

Example: Academic achievement, taste ranking, honors received, educational qualification etc.

           Interval scale has equal units of measurement, thus making it possible to interpret not only the order of scale scores but also the distance between them. It has the properties of identity, magnitude, and equal intervals. 

     

            Example: test scores, height (in cm), Intelligent Quotient (IQ) and many more.

Ratio scale has the property allows one to make statements of equality of intervals. This is the highest level of measurement which includes the inherent zero starting point. 

Examples: number of children in a family, student enrolment income and many more.