This module describes common experimental designs used in quasi-experimental research.

Learning Objectives

• List and describe the common experimental designs used in quasi-experimental research
• Provide examples of quasi-experimental projects that utilize these experimental designs

In the following SlideShare, Quasi-Experimental Research Designs, the most basics experimental designs most used in quasi-experimental research are discussed. These designs will be discussed in more detail in the remainder of this module.

QUASI EXPERIMENTAL DESIGN from MAHESWARI JAIKUMAR

True experimental research is considered the gold standard because subjects are randomly assigned to the treatment and control groups. However, often times, especially in social science research, the random assignment of subject is not possible, practical or ethical. Quasi-experimental designs offer an alternative that allows the research to continue and still produce valid results. The quasi-experimental research designs can be divided into three basic categories:

Non-Equivalent Control Groups

This type of design includes at least one experimental group and one control group used for comparison. This design often uses already existing groups or creates groups out of convenience because randomization is not possible. For example, if a study was examining the impact of a new teaching style on learning in two 5^th grade classrooms, it would be disruptive to re-arrange the classrooms to randomize the subjects, therefore existing groups are used. The disadvantage is that there may be inherent differences between two groups from the outset that may bias or skew the results of the study. There are also matching methods used to create comparison groups through different methods of “matching” the characteristics of subjects in group A with the subjects selected to be the in-comparison group, group B. These methods involve the intentional selection of subjects and therefore, even though the experimental and control groups may be more similar using this method, it is still considered quasi-experimental. Methods for constructing a comparison group through matching will be discussed in the next module. Once the experimental and control groups have been identified and established, the groups may be tested and compared in a pre-test/post-test manner or in a longitudinal manner (time series) that involves comparing the results of both groups repeatedly tested over time.

Pre-Test/Post-Test No Control Group

In this type of design, the researcher has identified a single experimental group to receive a treatment. The entire group will be pre-tested, the treatment will be applied or given, and the entire group will be post-tested. If pre-treatment values differ significantly from the post-treatment values, the researcher can suggest that the change in values was due to the treatment. Because researchers typically manipulate or apply the treatment to the entire group, the sample size is often larger which increases the validity of the results. An example would be if a researcher wanted to test the effects of caffeine on heart rate. He or she would check the heart rates of the entire test group, administer the pre-determined dosage of caffeine, and then check the heart rates again.

Time-Series

A time series design is one in which the researcher observes or tests one group of subjects repeatedly both before and after the administration of treatment. This type of design is chosen when attempting to demonstrate long term effects. For example, if a school district wanted to examine the effects of a new curriculum on standardized test scores, it would be useful to examine the yearly test scores for a period of years both before and after the adoption of the new curriculum. Examination of several years of test scores prior to the new curriculum helps establish a baseline that can be compared with results over time following the treatment. The time series design can be improved by adding comparison with a control group that does not receive the treatment.

Suggested Readings

Bernard, H. R., & Bernard, H. R. (2012). Social research methods: Qualitative and quantitative approaches. Sage.
Brown, L. (2010). Quasi-experimental research. Doing Early Childhood Research: International perspectives on theory and practice, 345.
Campbell, D. T., & Stanley, J. C. (2015). Experimental and quasi-experimental designs for research. Ravenio Books.
Creswell, J. W. (2013). Research design: Qualitative, quantitative, and mixed methods approaches. Sage publications.
Lipsey, M. W. (1990). Design sensitivity: Statistical power for experimental research (Vol. 19). Sage.
Punch, K. F. (2013). Introduction to social research: Quantitative and qualitative approaches. Sage.
William R.. Shadish, Cook, T. D., & Campbell, D. T. (2002). Experimental and quasi-experimental designs for generalized causal inference. Wadsworth Cengage learning.