Learning Objectives
- Discuss when is the appropriate time to use a pre-experimental Design.
- Identify and describe the various types of pre-experimental designs.
What is it and When to Use it?
Time, other resources such as funding, and even one’s topic may limit a researcher’s ability to use a solid experimental design such a a between subject (which includes the classical experiment) or a within subject design. For researchers in the medical and health sciences, conducting one of these more solid designs could require denying needed treatment to patients, which is a clear ethical violation. Even those whose research may not involve the administration of needed medications or treatments may be limited in their ability to conduct a classic experiment. In social scientific experiments, for example, it might not be equitable or ethical to provide a large financial or other reward only to members of the experimental group. When random assignment of participants into experimental and control groups (using either randomization or matching) is not feasible, researchers may turn to a pre-experimental design (Campbell & Stanley, 1963).Campbell, D., & Stanley, J. (1963). Experimental and quasi-experimental designs for research. Chicago, IL: Rand McNally. However, this type of design comes with some unique disadvantages, which we’ll describe as we review the pre-experimental designs available.
Types
If we wished to measure the impact of some natural disaster, for example, Hurricane Katrina, we might conduct a pre-experiment by identifying an experimental group from a community that experienced the hurricane and a control group from a similar community that had not been hit by the hurricane. This study design, called a static group comparison, has the advantage of including a comparison control group that did not experience the stimulus (in this case, the hurricane) but the disadvantage of containing experimental and control groups that were determined by a factor or factors other than random assignment. As you might have guessed from our example, static group comparisons are useful in cases where a researcher cannot control or predict whether, when, or how the stimulus is administered, as in the case of natural disasters.
In cases where the administration of the stimulus is quite costly or otherwise not possible, a one-shot case study design might be used. In this instance, no pretest is administered, nor is a control group present. In our example of the study of the impact of Hurricane Katrina, a researcher using this design would test the impact of Katrina only among a community that was hit by the hurricane and not seek out a comparison group from a community that did not experience the hurricane. Researchers using this design must be extremely cautious about making claims regarding the effect of the stimulus, though the design could be useful for exploratory studies aimed at testing one’s measures or the feasibility of further study.
Finally, if a researcher is unlikely to be able to identify a sample large enough to split into multiple groups, or if he or she simply doesn’t have access to a control group, the researcher might use a one-group pre-/posttest design. In this instance, pre- and posttests are both taken but, as stated, there is no control group to which to compare the experimental group. We might be able to study of the impact of Hurricane Katrina using this design if we’d been collecting data on the impacted communities prior to the hurricane. We could then collect similar data after the hurricane. Applying this design involves a bit of serendipity and chance. Without having collected data from impacted communities prior to the hurricane, we would be unable to employ a one-group pre-/posttest design to study Hurricane Katrina’s impact.
Table 7.2 summarizes each of the preceding examples of pre-experimental designs.
Table 7.2 Pre-experimental Designs
| |
Pretest |
Posttest |
Experimental group |
Control group |
| One-shot case study |
|
X |
X |
|
| Static group comparison |
|
X |
X |
X |
| One-group pre-/posttest |
X |
X |
X |
|
As implied by the preceding examples where we considered studying the impact of Hurricane Katrina, experiments do not necessarily need to take place in the controlled setting of a lab. In fact, many applied researchers rely on experiments to assess the impact and effectiveness of various programs and policies.
KEY TAKEAWAYS
- Pre-experimental designs are not ideal, but have to be done under certain circumstances.
- There are three major types of this design.
