Scientific Thinking
Independent vs Dependent Variable
Every experiment has variables you control and variables you observe. Telling the independent from the dependent variable is the first step in reading or designing a study.
| Aspect | Independent variable | Dependent variable |
|---|---|---|
| What it is | The factor you change or set | The outcome you measure |
| Also called | The cause / input / predictor | The effect / output / response |
| Who controls it | The experimenter | It responds to the independent variable |
| On a graph | Usually the x-axis | Usually the y-axis |
| Example | Amount of fertiliser given | Plant height that results |
When to use independent variable
The independent variable is what you deliberately vary to see its effect — the one thing you change between conditions while keeping others constant.
When to use dependent variable
The dependent variable is what you record to detect that effect — the measured outcome that "depends on" the independent variable.
Frequently asked questions
- How do I remember which is which?
- The dependent variable "depends on" the independent one. You change the independent variable and measure how the dependent variable responds. A memory aid: "I change the Independent; I Depend on it to see the effect."
- What are controlled variables?
- Controlled variables are the other factors you deliberately keep constant so they can’t muddy the result. Holding them steady is what lets you attribute a change in the dependent variable to the independent one.
- Can there be more than one of each?
- Yes. Studies often manipulate several independent variables or measure several dependent variables, though simple experiments keep to one of each so the effect is clear.