Pre-Experimental Designs

In pre-experimental designs, either a single group of participants or multiple groups are observed after some intervention or treatment presumed to cause change. Although they do follow some basic steps used in experiments, pre-experimental designs either fail to include a pretest, a control or comparison group, or both; in addition, no randomization procedures are used to control for extraneous variables. Thus, they are considered “pre-,” indicating they are preparatory or prerequisite to true experimental designs. Pre-experimental designs represent the simplest form of research designs. Together with quasi-experimental designs and true experimental (also called randomized experimental) designs, they make the three basic categories of designs with an intervention. Each contains subdesigns with specific strengths and weaknesses.

Because the validity of pre-experimental designs is threatened by inadequate control during implementation, it is difficult or impossible to rule out rival hypotheses or explanations. Therefore, researchers should be especially cautious when [Page 1082]interpreting and generalizing the results from pre-experimental studies. However, pre-experimental designs are cost-effective ways to explore whether a potential intervention merits further investigation. They might be particularly useful when there are less than perfect conditions for true experimental designs. These may include the restraints of time, space, participants, resources, and ethical issues; logistical constraints, such as the investigation of a small atypical sample; or the evaluation of a previous intervention without adequate planning of the research design. Under those circumstances, as long as appropriate caution is taken while making interpretations and generalizations, results from pre-experimental designs could still be suggestive to the field and future research.

This entry first describes the notations used to diagram pre-experimental designs. Next, this entry discusses the major types of pre-experimental designs and possible improvements to these designs. The entry concludes with a brief presentation of the limitations and benefits of pre-experimental designs.