The meaning of "quasi" is "pseudo, self-styled (sort of)." Thus, this experimental design is considered non-scientific and unreliable by researchers in pure science fields such as medical and biology science.
So why do researchers conduct this research design? Quasi-experimental research attempts to examine the effects of an intervention on a specific population; it aims to determine whether a program or intervention has the intended effect on a study's participants (NCTI www.nationaltechcenter.org).
There are many types of quasi-experiments. Here are a few of the most common (Trochim, 2006 and NCTI, [n.d.]):
- Pretest-Posttest design study without a control group: collect data on study participants' level of performance before the intervention took place (pretest), and again collect the same data after the intervention took place (posttest). This study only looks at one group of individuals who receive the intervention.
- Pretest and posttest design with a control group ("non-equivalent groups design): An existing group of participants receive a treatment (treatment group), and another existing group of participants to serve as a control (or comparison) group. Participants are not randomly assigned to conditions, but rather are assigned to the treatment or control conditions along with all the others in their existing group.
- Interrupted time-series designs: This study design is similar to a pretest-posttest design but with multiple pretests and multiple posttests.
National Center for Technology Innovation (NCTI) (n.d.), Quasi-experimental study. Retrieved October 16, 2011 from: http://www.nationaltechcenter.org/index.php/products/at-research-matters/quasi-experimental-study/
Trochim, William M.K. (2006), Research method knowledge base: Quasi-experimental design. Retrieved October 16, 2011 from http://www.socialresearchmethods.net/kb/quasiexp.php
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