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What Is the Control & Independent Variable of an Experiment?

Science is the process of predicting an outcome and then testing to see if the prediction was accurate, which is how scientific laws are forged. However, in any given experiment there are numerous factors which could cloud the results. By isolating certain variables, scientists can study their independent relationship to an observable process, which requires the use of control and independent variables.

Design of Experiments
- The design of an experiment (DOE) is a process by which experimental data can be collected in an accurate and efficient manner. The goal of the process is to create a database of empirical results that can be analyzed to yield compelling and unbiased conclusions regarding a hypothesis. For example, a hypothesis may be formed that states the volume of a gas will expand as its temperature rises. An experiment could then be designed to test the relationship between the volume of a gas and its temperature.
Control Variables
- Control variables are experimental factors that may affect the outcome of an experiment, but for which the experimenter does not wish to consider in terms of the overall experimental output, which is accomplished by balancing the variables effect across the range of independent variables tested. In other words, control variables are kept constant throughout the experiment, thereby eliminating their impact on the results. In the case of the gas experiment, the pressure of the gas would be a control variable. The pressure of the tested gas would be kept at a constant pressure regardless of temperature, eliminating the dynamic effect of varying pressure.
Independent Variables
- Independent variables are the active factors that are varied during the experiment. They represent the factors that are measured and modified by the experimenter to determine their relationship to an observed outcome. By eliminating other factors through the use of control variables, these factors can be isolated and studied. In the case of the gas experiment, the temperature of the gas would be an independent variable. The temperature of the tested gas would be modified, by increasing or lowering it, to determine its effect on the volume of the gas.
Experimental Outcome
- The design of an experiment is used to derive empirical models that link the output of the experiment, in this case volume, to the input of the experiment, which is temperature in this example. By using control variables, the experimenter negates the influence of these factors, in this case pressure, on the experimental results, allowing the experimenter to derive a direct relationship between the independent variable and the experimental outcome. This relationship will either support or refute the experimenter's original hypothesis.

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