uses an experimental group and a control group to test a hypothesis.

In this type of research, study subjects (whether animal or human) are selected according to relevant characteristics, and then randomly assigned to either an experimental group, or a control group. Random assignment ensures that factors known as variables, which may affect the outcome of the study, are distributed equally among the groups and therefore could not lead to differences in the effect of the treatment under study. The experimental group is then given a treatment (sometimes called an intervention), and the results are compared to the control group, which does not receive treatment. A placebo, or false treatment, may be administered to the control group. With all other variables controlled, differences between the experimental and control groups may be attributed to the treatment under study.

An experimental design with two or more randomly selected groups (an experimental group and control group) in which the researcher controls or introduces the independent variable and measures the dependent variable at least two times (pre- and post-test measurements).

"Controlled Experiment" is an episode of the original The Outer Limits television show. It first aired on 13 January, 1964, during the first season.