Although both experimental and quasi-experimental designs attempt to explore a relationship between variables, the way each research methodology explores this relationship differs. One of the main differences between experimental and quasi-experimental studies is the use of random assignment. According to Gasparrini and Bernal (2015) quasi experiments do not use random assignment. However, experimental designs rely heavily on random assignment, making this one of the key factors that differentiates the two methodologies (Newman, 2011).
Another difference between experimental studies it that one variable is manipulated, and one variable is untested (the control group). In contrast, a quasi-experimental design uses pre-existing conditions that are not measured. Furthermore, the pre-existing conditions used in quasi-experimental designs are not measured or manipulated. Newman (2011) further concurs in arguing that because these variables are not manipulated, there is no way for the researcher to make casual statements about their relationship.
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"Experimental vs Quasi Designs".
There are many ways that a researcher can manipulate an independent variable. For example, the researcher could make the room hot or cold, leave participants in a small room for long periods of time, or even expose the independent variable to a stressor (such as being in a waiting room for an extended period with other individuals who are annoying) (Newman, 2011). Although these are just a few examples, the way the researcher manipulates the independent variable is heavily contingent on what he or she is trying to study. Yet, what the researcher is trying to study also dictates what type of methodology he or she uses.
For example, in studying the relationship between the violent movies and aggression in young children, a researcher could explore whether or not children who have been exposed to violent movies (in showing the children in a certain group a scary movie) are more likely to be aggressive. The control variable in this study would be measuring aggression in children who have not been shown a violent movie. This would allow the researcher to compare the differences between the two groups. Contrasting this example, a researcher may want to explore how living in an economically disadvantaged neighborhood affects the child’s emotional state. This research would use children from the economically disadvantage area, and would not be characterized by random assignment (Goodnight, Lahey, and Bejamin, 2012).
