Experimental and Quasi-Experimental Research Designs

The experimental research design is one of the most reliable quantitative designs available. Basically, it requires that the researcher conduct an actual experiment in order to prove the research hypothesis. Similar yet fundamentally different from the experimental design is the quasi-experimental design. his paper discusses the procedure in conducting an experimental design research and differentiates it from a quasi-experimental research design. Examples of each are given to facilitate further comparison and contrast. The first step in conducting an experimental research design is to identify the independent and dependent variables.

According to Random House’s dictionary of statistical terminologies, “the dependent variable is the event studied and expected to change when the independent variable is changed. ” (Random House, 2001, p. 534). In Butler and Lijinsky (2005) which is an example of experimental research, the independent variable was the type of rat while the dependent variable was the toxicity level. This meant that the research seeks to verify whether different types of rats would have different acute toxicity levels.

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After the identification of the independent and dependent variables, the next step is to randomly select a sample for the experiment.

To randomly select a sample means to make sure that all of the members of the population have an equal chance of being selected (Corder &Foreman, 2009). For example, when seeking to study a school population as is the case in of Stevens & Slavin (1995), random sampling is conducted by placing all of the possible respondents in a list and selecting from that list randomly. In this way, each student has an equal opportunity to be selected for the study.

Lastly, once the experiment is conducted, a secure atmosphere is generated wherein the effect of other factors are minimized (Mertens, 1998).

Going back to Butler and Lijinsky (1995), the experiment was conducted in a secure atmosphere where the only variables were the type of rat and the toxins induced to them. All other factors such as the food they were given, the space of their cages and so on were kept the same for the different types of rat. In a quasi-experimental approach, an experiment is also conducted and dependent and independent variables are also selected. Measures to keep all other variables constant are also taken. However, the defining difference between the tow is that quasi-experimental designs do not conduct random sampling (Mertens, 1998).

For example, the quasi-experimental research conducted by Dutton (1986) simply a sample from those that were available. This is not random sampling and therefore the design cannot be considered as experimental but it does fit the quasi-experimental description. In conclusion, it is clear that while experimental and quasi-experimental research designs are similar, they do have an essential difference.

References

Butler, A, and Lijinsky, W. (2005). “Acute toxicity of aflatoxin G1 to the rat” Journal of Pathology, 102 (4), 209-212. Corder, G. , Foreman, G. (2009). Nonparametric Statistics for Non-Statisticians: A Step-by-Step Approach. Wiley. Dutton, D. (1986). “The Outcome of Court-Mandated Treatment for Wife Assault: A Quasi-Experimental Evaluation. ” Violence and Victims, 1(3) 163-175 Mertens, D. (1998). Research methods in education and psychology: Integrating diversity with quantitative & qualitative. Sage. Random House. (2001). Random House Webster's Unabridged Dictionary. Random House, Inc. Stevens, R. , and Slavin, R. (1995). Effects of a Cooperative Learning Approach in Reading and Writing on Academically Handicapped and Nonhandicapped Students. The University of Chicago Press.