In a previous post, we began a discussion on variables. In this post, we will continue our journey in understanding variables by looking at the family of variables. We will look at the following

• Dependent variable
• Independent variable
• Measured variable
• Controlled variable
• Treatment variable

Dependent Variable

Dependent variables are variables whose outcome is influenced by the independent variable.They go by many names in research such as criterion, effect, outcome, and or consequence variable. It is important to know the many different names for a dependent variable in order to avoid becoming confusing when reading research.

When looking at research questions, it is possible to identify the dependent variable by looking at a question that is focused on the outcome of the study.

Independent Variables

Independent variables are variables that influence the dependent variable. Other names for independent variable include treatment, factors, determinants, antecedents, and predictors. Below is an example of a research question using independent and dependent variables.

Do students who spend more time studying math have higher grades than students who spend less time studying? 
Independent variable: study time     Dependent variable: grade

This example above wants to see how study time (independent variable) influences the outcome of math grades (dependent variable).

Types of Independent Variables

There is a great deal of variety not only in the names of independent variables but also in the types. Below are some independent variables with examples when appropriate.

Measured variable. This is an independent variable that is observed or measured by the researcher. A research question example would be “How does verbal ability influence GPA in college?” You measured verbal ability in this example.

Control variable. Researchers include control variables in order to neutralize their influence on the dependent variable. This is done because the controlled variable is not the focus of explaining the dependent variable. Control variables are often demographic traits such as race, gender, socioeconomic status, etc. By removing the influence of control variables a researcher is able to obtain a clearer picture of how the independent variables of the study influence the dependent variables.

Treatment variable. For experimental studies, you will use treatment variables. These variables are categorical. This is because one group receive the “treatment” while another does not. The desire is to see if the treatment makes a difference in the dependent variable. Below is a research question that indicates a treatment variable

How does pop music influence reading comprehension?
Independent variable: Music        Dependent variable: reading comprehension

Within the independent treatment variable, there need to be at least two levels or groups. One group might hear pop music and the other group might not hear pop music. Both groups would take some sort of assessment to measure their reading comprehension. Your desire is to see if there is a difference between the groups. If there is you could contribute this difference to the effect of music which is what you used as a treatment for one group in the experiment.

Conclusion

Variables serve the purpose of allowing a researcher to examine a phenomenon quantitatively. The type of variable used depends on the purpose of the study. Each type of variable comes with certain rules that indicate when it is applicable to use it. This is important for researchers to know when deciding on the research design of their project.