A variable is any factor, trait, or condition that can differ. An experiment usually has three kinds of variables: independent, dependent, and controlled.
- The independent variable is controlled by the scientist.
- The dependent variable changes, depending on the independent variable. This is measured by the scientist to prove or disprove their hypothesis.
- The controlled variables are conditions which must be kept controlled and constant throughout the experiment so that they don't interfere with the dependent variable. When the experiment is repeated, the controlled variables must be exactly the same.
Figure 1: Example of experimental variables for a drought experiment.