Control group

A group in an experiment that does not receive the tested intervention and provides a comparison baseline for estimating its effects.

Randomized controlled trial: An experiment that randomly assigns participants to intervention and comparison groups to estimate causal effects. Random assignment makes differences between the control group and intervention group less systematic.
Independent variable: A variable deliberately changed or assigned to examine its effect on another variable. The control group's defining feature is not receiving the independent variable's tested intervention.
Active control: A comparison condition that receives an established intervention rather than no treatment or an inert placebo. It compares a new intervention with existing care instead of with an untreated baseline.
Clinical trial: A prospective study that evaluates health interventions in human participants. Control groups help clinical trials distinguish treatment effects from natural change and other influences.
Hawthorne effect: Changes in behavior associated with awareness of being observed or studied. Control participants who know they are studied may change behavior even without the intervention.
Placebo: An inactive treatment designed to resemble an active treatment in appearance or administration. A placebo can make a control group comparable in expectations and treatment experience.
Dependent variable: A measured outcome whose variation is studied in relation to an independent variable. The same outcome must be measured comparably in control and intervention groups.
Placebo-controlled trial: A clinical trial that compares an intervention with an inactive treatment designed to mimic it. This specific design uses a placebo as the control condition.
Cluster randomized trial: A trial that assigns groups such as schools or clinics, rather than individuals, to study conditions. Its control groups consist of clusters assigned to the comparison condition.
Regression to the mean: The tendency for unusually extreme measurements to be followed by measurements closer to the average. A control group helps reveal whether apparent improvement would occur without treatment.

Linked from 9 pages