A control group allows a scientist to compare it to the other group or groups in an experiment. If a scientist notices a significant difference between the control group and one or more of the other groups, he can logically lead to the conclusion that the independent variable has an impact on the dependent variable.
Then, what is the purpose of a control condition?
A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable. This increases the reliability of the results, often through a comparison between control measurements and the other measurements.
Why is it important to use a control in experiments?
A control is a part of the experiment that tests whether the system behaves as it should. Imagine that you want to measure the rate of an enzyme reaction. This is done by using an assay for the appearance of the reaction products. Controls serve two somewhat related purposes in an experiment.
What is the purpose of a positive control?
A positive control is a group in an experiment that receives a treatment with a known result, and therefore should show a particular change during the experiment. It is used to control for unknown variables during the experiment and to give the scientist something to compare with the test group.