A “fair test” refers to an experiment that is carefully controlled to ensure that the information gathered is reliable. Fair tests are used in the fields of science, psychology and medicine, among other disciplines. To guarantee the validity of an experiment, a control group is utilized, biases are limited, interfering variables are controlled and an adequate sample size is used.
A control group is used to give the results of the experimental group a standard to which to compare them. In an experiment to determine the effectiveness of a particular medication in relieving headaches, for example, the control group receives a placebo. To prevent biases, the participants are not told whether or not they are getting the actual medication. If participants in the control group know that they are taking a placebo, they might monitor their headaches less intently.
A large sample size of participants is required, because if there are too few people in the control and experimental groups, the statistical margin of error overwhelms the results of the test.
All participants in the experiment also agree to control variables that could lessen or increase headaches, like diet and exercise. This prevents those variables from interfering with the results.