Control Condition Definition
The control condition in an experimental design lacks any treatment or manipulation of the independent variable. People assigned to the control group serve as the basis of comparison for the people in the experimental condition. Everything in a control condition is the same as the experimental conditions except that the independent variable is absent or held constant. Assuming that the groups were equivalent prior to the treatment, any differences between the control condition and the experimental condition can be attributed to the effect of the independent variable.
Control Condition Evidence and Implications
The control condition is designed to be equivalent to the experimental condition except for the independent variable, which is absent or held constant under its normal circumstances. Thus, the control condition provides a basis for comparison. The researcher assesses the influence of the independent variable by comparing the outcomes under the experimental and control conditions. For example, if researchers were to design an experimental study to test the effect of loud music on test performance, students who did not listen to loud music would be in the control group. The researchers could compare the test score of the students who did listen to loud music with the students in the control group to determine whether loud music had an impact on test scores.
Not all experimental designs have a control condition. However, it is useful to include a control condition to determine the effect of the procedure outside the effect of the independent variable. Consider the design of an experiment in which researchers are testing the effectiveness of two different types of medicine on headache relief. Participants with headaches would be divided into two groups, with each group getting one type of medicine. After an hour, researcher would ask participants to rate the effectiveness of the headache medicine. From this design, researchers could determine if one of the medicines was more effective that the other. They could not determine, however, if either of these medicines was more effective than no medicine at all. It is possible that simply believing you are taking headache medicine can lessen the pain. If the researchers included a control condition in this experimental design, they could make this comparison. Participants could be divided into three groups, with two groups receiving different headache medicines and one group receiving a placebo.
Then, researchers could compare the effectiveness ratings of the two real headache medicines with the ratings from the control group. If the effectiveness ratings provided by participants receiving actual medicine were greater than those provided by participants in the control group, researchers could conclude that taking a headache medicine was more effective than taking no medicine. Thus, including a control condition allows researchers to compare the way things are in the presence of an independent variable with the way things would have been in the absence of an independent variable.
- Pelham, B. W., & Blanton, H. (2002). Conducting experiments in psychology: Measuring the weight of smoke (2nd ed.). Belmont, CA: Wadsworth.