A controlled variable, also known as a constant variable or control variable, is an element that is kept constant and unchanged throughout an experiment to ensure accuracy and reliability of the results. It is not part of the experiment, and it is not an independent or dependent variable. Control variables are important to identify in experiments because they can change the outcome of an experiment in a way that makes it invalid. Control variables must be kept constant to prevent them from influencing the effect of the independent variable on the dependent variable. In any system existing in a natural state, many variables may be interdependent, with each affecting the other. Scientific experiments test the relationship of an independent variable to the dependent variable. Any additional independent variable can be a control variable. In an experiment, a researcher is interested in understanding the effect of an independent variable on a dependent variable. Control variables help ensure that the results are solely caused by the experimental manipulation. To control variables, researchers can hold them constant at a fixed level using a protocol that they design and use for all participant sessions.