What are quasi-experiments? Name and describe two different quasi-experimental designs.
What will be an ideal response?
Ans: Quasi-experiments, also referred to as natural experiments, allow comparisons to be made in observations across time and among groups, with the assumption that these groups may not be equivalent to each other. They differ from true experiments in that they lack random assignment. The different quasi-experimental designs include pretest–posttest, interrupted time series design, nonequivalent control group design, and control time series design.
Pretest–posttest ? Initial observations are taken (the pretest), the treatment (e.g., an intervention) is implemented, and observations are taken again (the posttest) so that a comparison can be made between what happened before the treatment and what happened after the treatment.
Interrupted time series design ? This is an extension of the pretest–posttest design. With this design, a number of observations are taken over time before a treatment (i.e., the interruption) is administered, and then, a number of observations are taken afterward. With this design, we can detect any pattern of behavior occurring before the treatment and whether the treatment affected this pattern.
Nonequivalent control group design ? This design improves upon the pretest–posttest design as it includes a control group. However, unlike with a true experiment, random assignment is not used; the control group usually is a preexisting group and is not assumed to be equivalent to the treatment group. This approach involves a nonequivalent control group in which the treatment group is compared with a nonequivalent control group.
Control time series design ? This design improves upon the interrupted time series design. With this design, a nonequivalent control group is added. This involves a series of the same observations for the control as for the treatment group but without exposure to the treatment.
Cognitive Domain: Analysis
Answer Location: Research Design: Quasi-Experiments
Difficulty Level: Medium
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