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True Experiment
Experiment in which subjects are assigned randomly to an experimental group that receives a treatment or other manipulation of the independent variable and a comparison group that does not receive the treatment or receives some other manipulation. Outcomes are measured in a posttest.
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Experimental Group
In an experiment, the group of subjects that receives the treatment or experimental manipulation.
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Comparison Group
In an experiment, a group that has been exposed to a different treatment (or value of the independent variable) than the experimental group.
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Control Group
A comparison group that receives no treatment.
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Posttest
In experimental research, the measurement of an outcome (dependent) variable after an experimental intervention or after a presumed independent variable has changed for some other reason.
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Pretest
In experimental research, the measurement of an outcome (dependent) variable prior to a change in a presumed independent variable for some other reason. The pretest is exactly the same "test" as the posttest, but administered at a different time.
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Randomized Comparative Change
The classic true experimental design in which subjects are assigned randomly to two groups; both these groups receive a pretest, one group then receives the experimental intervention, and then both groups receive a posttest. Also called the posttest-only control group design. Also known as a pretest-posttest control group design.
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Randomized Comparative Pottest Design
A true experimental design in which subjects are assigned randomly to two groups -- one group then receives the experimental invention and both groups receive a posttest; there is not pretest.
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Matching
A procedure for equating the characteristics of individuals in different comparison groups in an experiment. Matching can be done on either an individual or an aggregate basis. For individual matching, indiviauls who are similar in terms of key characteristics are paired prior to assignment, and then the two members of each pair are assigned to teh two groups. For aggregate matching, groups are chosen for comparison that are similar in terms of the distribution of key characteristics.
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Field Experiment
A study conducted in a real-world setting.
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Quasi-experimental Design
A reserach design in which there is a comparison group that is comparable to the experimental group in critical ways, but subjects are not randomly assigned to the comparison and experimental groups.
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Nonequivalent Control Group Design
A research design in which there is a comparison group that is comparable to the experimental group in the critical ways, but subjects are not randomly assigned to the comparison and experimental groups.
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