Variables are the heart of quantitative research. This post begins a discussion on the types of variables. This will prepare for understanding how to develop purpose statements, research questions, and hypotheses that involve the use of variables. In this post, we will look at
- Defining variable
- Categorical and continuous variable
- Variable vs construct
A variable is a trait or characteristic that is measurable and that varies. Common examples include height, weight, income, grade level, gender, etc. All of these examples of variables can be measured, which means that the information can be recorded by the researcher, and they vary, which means their values on individual cases are different. If the principle of measurement or variable is violated then the concept is not a variable.
Categorical and Continuous Variables
Variables can be measured in two common ways, either in categories or continuously. Categorical measurement is looking at a variable that has discrete groups that cannot overlap. An example would be gender. A person is either male or female and cannot be both. Categorical variables record the frequency of the occurrence of a variable.
Continuous variables measure a variable along a continuum or range. Examples include age, weight, and height. All of these variables can take on an infinite number of values. A persons weight could be 80kg, 81kg, 81.5kg, 90kg and on and on.
Variables vs. Construct
Two words commonly confused in research are variable and construct. A variable is a trait or characteristics that is stated in a specific way. An example would be a person’s blood pressure. This can be measured directly and it is possible for it to vary.
A construct, on the other hand, is a trait or characteristic that is stated in a general way. A construct is too abstract to be measured directly. An example of a construct would be health. You have to wonder how to measure the construct of health. One way would be to measure the variable of a person’s blood pressure as blood pressure is an indication of a person’s overall health. By measuring blood pressure, you are developing an understanding of the construct of health because of the known relationship between blood pressure and health.
Constructs help with the explanation of the results of different variables. What does it mean to have high blood pressure? Often it means that a person has poor health. What does it mean to have poor health? One example of poor health can be found by knowing a person’s blood pressure. Constructs also help us to lump together similar variables. If someone has a high weight, high blood pressure, and low amounts of exercise these are all indicators of poor health.
A construct must be based on a strong review of literature to assure it is theoretically sound. Anybody can make any construct they want. The difference between a good and bad construct is its relation to existing theories.
Variables are critical to quantitative research as they provide the concepts that are measured and varied. Variables can measure frequency or account for a continuum of responses. Variables can also be used to explain construct. As such, variables will be a topic that we will return to in the future as their use in research is almost the total focus of quantitative research.