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Quasi means as if or almost, so a quasi-experiment means almost a true experiment. Quasi-experiment is a research design with some characteristics of a true experiment. The element frequently missing in quasi-experiment research design is random assignment of subjects to the control and experimental conditions. Quasi-experiments are subject to concerns regarding internal validity, because the treatment and control groups may not be comparable at baseline. The intended purpose for doing quasi-experiment research is generally to capture longer time periods of different events to control for various threats to validity and reliability. Examples of quasi-experiment research design are the natural experiment or trend analysis. There are many varieties of quasi-experiment research designs, and there is generally little loss of prestige in doing a quasi-experiment instead of a true experiment, although you may run into someone who is biased against quasi-experiments.
In quasi-experiment, matching instead of randomized testing is used. In quasi-experiment, the word "trend" is used instead of cause, and we are interested in finding the one true trend. Because quasi-experiment research designs tend to involve many different, but interlocking relationships between variables. This allows identification of spurious and intervening variables. Spurious variables should be thrown out; intervening variables require multiplying the effects of two variables; and suppression refers to when part of a variable affects part of another variable even though the bivariate relationship is nonsignificant.
In quasi-experiment, time series analysis is involved. A time series is perhaps the most common type of longitudinal research found in criminal justice. In quasi-experiment the unit of analysis is often something different than people. Quasi-experiment is well suited for "fuzzy" or contextual concepts such as sociological quality of life, anomie, disorganization, morale, climate and atmosphere. Someone studying the effects of a new police strategy in town would try to find a similar town somewhere in the same geographic region. That other town would have citizen demography that are very similar to the experimental town. That other town is not technically a control group, but a comparison group, and this matching strategy is sometimes called nonequivalent group design.
The hope is that the design will generate stable, reliable findings and tell us something about the effects of time itself. In fact, for a noninterrupted time series, the independent variable is usually time itself. If you were monitoring rises and falls in crime rates and attributing it to changes in society over time. Quasi-experiment is somewhat creative or unusual in what it attributes the cause of something to, and this is the case because we aren't using a true experiment where we manipulate some independent variable in order to assess causality. Models also permit elaboration and specification. Many causal modeling techniques exist, from the simple use of crosstabulation tables to run partial correlation analysis to the more sophisticated, and rarely-seen technique of path analysis which is essentially a regression analysis run of each variable on every other variable. Some instructors think modeling is as a heuristic device for teaching research methods.
Randomized trials and quasi-experiments in education research: From NBER Reporter.
Experiments and quasi-experiments: methods for evaluating marketing options; hospitality managers could achieve greater success with marketing initiatives. Hotel & Restaurant Administration.
The Statistical Analysis of Quasi-Experiments. Christopher H. Achen ," American Journal of Sociology 95, no. 2 (Sep., 1989): 468-470.
Developing Team Cohesion: A Quasi-Field Experiment. by John F. Costello, Air Force Institute of Technology (U.S.). Research findings show that cohesion influences the job satisfaction, and health of military members, particularly under highly stressful conditions, such as those encountered in combat.