what is a positive control

A positive control is a group or sample in an experiment that is exposed to a treatment that has a known outcome. The purpose of a positive control is to show that the experiment was performed properly and to validate the experimental procedure. Positive controls are used to assess the test validity of the experimental protocol or equipment by producing the expected result. For example, in a bacterial growth experiment, a positive control would be a plate with a known type of bacteria that is expected to grow. Positive controls are particularly useful for validating the experimental procedure. In contrast, a negative control is a group or sample in an experiment that is not exposed to the experimental treatment or to any other treatment that is expected to have an effect. Negative controls are used to assess the effects of variables other than the independent variable and to eliminate alternate explanations of experimental results. By not exposing the negative control group to the experimental treatment or any other treatment, they are not expected to produce any result due to any variable in the experiment and may serve as the “baseline” .