What Are Independent and Dependent Variables?
A variable is anything that can take different values in a study, such as age, test score, temperature or income. Two kinds matter most in research design: the independent variable, which the researcher changes or compares, and the dependent variable, which is the outcome that is measured. Understanding them is a basic step in designing and reading studies.
The definitions
- Independent variable (IV): the factor that is manipulated, or the predictor that is thought to influence something else. It is also called the explanatory or predictor variable.
- Dependent variable (DV): the outcome or response that is measured to see whether it changes. It is also called the outcome variable.
The dependent variable "depends" on the independent variable, at least in the researcher's hypothesis.
Examples
| Research question | Independent variable | Dependent variable |
|---|---|---|
| Does sleep affect exam performance? | Hours of sleep | Exam score |
| Does a new teaching method improve reading? | Teaching method | Reading test score |
| Does fertilizer change plant growth? | Amount of fertilizer | Plant height |
| Do social media hours relate to loneliness? | Hours of use | Loneliness scale score |
Other types of variable
- Control variables: held constant to avoid confusing the results, such as the same room and time in an experiment.
- Confounding variables: unmeasured or uncontrolled factors that affect both the independent and dependent variables, and can distort conclusions.
- Moderating variables: change the strength of the relationship between the IV and DV.
- Mediating variables: explain how or why the IV affects the DV.
Types of measurement
Variables can be categorical, such as gender or treatment group, or numerical, such as age or income. Whether a variable is nominal, ordinal, interval or ratio affects which statistics are appropriate.
In experiments and observational studies
In experiments, researchers manipulate the independent variable and randomly assign participants to conditions, which allows stronger claims about cause. In observational studies, researchers measure variables as they occur and cannot control them, so associations are harder to interpret.
Tips for identifying them
- Find the research question or hypothesis.
- Ask what is being changed or compared, and what is being measured.
- Write the relationship: "The effect of X on Y."
- Check for control and confounding variables.
Why it matters
Clear variables make your research question testable, guide your method and help you choose statistics. Many assignments ask you to name them.
Related terms
See correlation vs causation, statistical significance, IRB, dissertation defense and primary source.
Frequently asked questions
How do I tell the independent variable from the dependent variable?
Ask which factor is thought to cause or influence the other. The cause or predictor is independent, and the outcome that is measured is dependent.
What is a control variable?
A factor that is kept constant so that it does not affect the results, helping to show that changes in the dependent variable come from the independent variable.
Can a study have more than one independent variable?
Yes. Many studies test several, for example the effect of both dose and age on recovery, and may examine how they interact.