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Scientific control

“When performing an experiment, a researcher wants to be certain that the variables or factors of interest are the only things affecting the outcome. Such extraneous variables include researcher bias, environmental changes, and biological variation. Scientific controls ensure that data are valid, and are a vital part of the scientific method.

An experiment which uses controls is called a controlled experiment, and usually separates research subjects into two groups: An experimental group and a control group. The control group is practically identical to the treatment group, except for the single variable of interest whose effect is being tested.

Controls are needed to eliminate alternate explanations of experimental results. For example, suppose a researcher feeds an experimental artificial sweetener to sixty laboratory rats and observes that ten of them subsequently die. The underlying cause of death could be the sweetener itself or something unrelated. Other variables, many of which may not be readily obvious, may interfere with the experimental design. For instance, perhaps the rats were simply not supplied with enough food or water, or the water was contaminated and undrinkable, or the rats were under some psychological or physiological stress, etc. Eliminating each of these possible explanations individually would be time-consuming and difficult. Instead, the researcher can use an experimental control, separating the rats into two groups: one group that receives the sweetener and one that does not. The two groups are kept in otherwise identical conditions, and both groups are observed in the same ways. Now, any difference in morbidity between the two groups can be ascribed to the sweetener itself—and no other factor—with much greater confidence.”

 

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