What defines the independent variable in an experiment?

The independent variable in an experiment is defined as the variable that is changed or manipulated by the experimenter. This is the factor that researchers intentionally alter to observe its effects on other variables, typically the dependent variable. For instance, if an experiment is designed to test how different amounts of sunlight affect plant growth, the amount of sunlight would be the independent variable since it is what the researcher changes.

In contrast, the controlled variable refers to aspects of the experiment that are kept constant to ensure a fair test, while the measured variable is the dependent variable, which is observed and recorded as it responds to changes in the independent variable. Constant variables maintain the validity of the experiment by ensuring that any changes in the dependent variable can be attributed solely to the manipulation of the independent variable. Thus, the focus on the independent variable is essential in understanding cause-and-effect relationships within experimental research.