3P.6—Variables and controls

The independent variable is deliberately changed; the dependent variable is measured; controlled variables are kept constant so that the response can be attributed fairly.

Write the independent variable with its levels or range, the dependent variable with its unit and method, and the key controls that could otherwise affect the outcome. Include a control group when a baseline is needed.

In a plant mineral experiment, calcium concentration is independent, mass change is dependent, and seedling age, light, volume, temperature and the other ions are controlled. A complete mineral broth provides a comparison.

A variable can be measured without being independent. Time may be controlled or used as an axis depending on the design; classify it from the actual question, not from the word alone.