What is Quasi-experimental design?
What is quasi-experimental design?
A quasi experimental study aims to demonstrate causality between an intervention and an outcome however lacks the element of random assignment to treatment or control groups. Quasi experiments share similarities with experimental design or random controlled trials however, quasi experiments typically allow the researcher to control the assignment conditions. Typically, these experimental designs are used when the variable the researcher intends to study cannot be manipulated due to practical or ethical reasons. These experiments are used extensively in social sciences and psychology.
One of the most common research methods is the Nonequivalent Groups design. This is a pretest-posttest design where the variables are measured prior to the experiment and post experiment so that the researcher can assess the overall effectiveness of a treatment. This type of design is a comparison of treatment and control groups that are assumed to be similar however these groups were not chosen through random assignment. One drawback to this design is that, as groups are not randomised, groups can be different prior to the study, affecting the outcome. This design is also especially susceptible to internal validity – a measure of the approximate truth about inferences regarding the causal relationship determined by the degree a study minimises error or bias.
Quasi-experiments have many advantages; they allow the researcher to attempt to determine a cause-and-effect relationship even when there are limitations to the study, they can reduce time and resources, as well as reinforcing the findings from other studies. However, as there is no randomisation in test groups and reduced internal validity, conclusions are less definitive in comparison to true experimental designs.