Control samples are an important part of the scientific method. Using a control group allows the person conducting the experiment to isolate the effect of the experimental treatment. If there is no control group, or the control group is imperfect, then the results of the experiment are less clear and may even be misleading. It is important to use as powerful control samples as possible to eliminate the effect of outside variables in experiments.
The Scientific Method
Scientist who conduct experiments according to the scientific method must use a particular sequence of steps. First, they must decide on a research question to investigate, such as whether a particular new medication helps with cold symptoms. Next they develop a hypothesis, which is an educated guess as to the effect of the treatment. In this case, they decide the new medication should work to alleviate symptoms. Then the researcher designs an experiment, such as testing out the medication on people with colds. The researcher carries out the experiment, records the conditions and results, and decides whether the results agree with the hypothesis.
Each experiment will be testing some kind of treatment or intervention, which is expected to have a particular effect. In this example, using the new medication is the treatment. In the experiment, the scientists will pick a group of people with colds and ask them to take the medication, and then record whether they got better. This is called testing the hypothesis -- the scientists want to know whether their initial guess was a correct assessment of the true effect of the treatment.
However, many other factors can be in play, aside from the experimental treatment. For example, people get better from colds naturally over time, whether or not they take any medication. They also might get better at different rates if they live in different environments or eat different foods. Their prior health also affects their recovery -- someone who is in poor health already will take longer to recover from a cold than a healthy person.
Using Control Groups
Therefore, scientists conducting research will pick some group of subjects that are as close as possible to the rest of the ones in the experiment, with the sole difference being that they are not getting the treatment. In our example, the scientists would take two groups with the same age, health status, environment, and so on, trying to match them up as closely as possible. Then the scientists would give both groups a medication similar in appearance, except that one medication would be the new medication being tested and the other medication would be a dummy that does nothing. The result of using control groups is that the scientist can isolate the effect of the treatment, and avoid the problem of other variables affecting the result of the experiment.
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