Pre-Experimental
Design
Pre-experimental
designs are so named because they follow basic
experimental steps but fail to include a control
group. In
other words, a single group is often studied but no
comparison between an equivalent non-treatment group
is made. Examples
include the following:
The
One-Shot Case Study.
In this arrangement, subjects are presented
with some type of treatment, such as a semester of
college work experience, and then the outcome
measure is applied, such as college grades.
Like all experimental designs, the goal is to
determine if the treatment had any effect on the
outcome. Without
a comparison group, it is impossible to determine if
the outcome scores are any higher than they would
have been without the treatment.
And, without any pre-test scores, it is
impossible to determine if any change within the
group itself has taken place.
One
Group Pretest Posttest Study.
A benefit of this design over the previously
discussed design is the inclusion of a pretest to
determine baseline scores.
To use this design in our study of college
performance, we could compare college grades prior
to gaining the work experience to the grades after
completing a semester of work experience.
We can now at least state whether a change in
the outcome or dependent variable has taken place.
What we cannot say is if this change would
have occurred even without the application of the
treatment or independent variable.
It is possible that mere maturation caused
the change in grades and not the work experience
itself.
The
Static Group Comparison Study.
This design attempts to make up for the lack
of a control group but falls short in relation to
showing if a change has occurred.
In the static group comparison study, two
groups are chosen, one of which receives the
treatment and the other does not.
A posttest score is then determined to
measure the difference, after treatment, between the
two groups. As
you can see, this study does not include any
pre-testing and therefore any difference between the
two groups prior to the study are unknown.
Table
5.1: Diagrams of Pre-Experimental Designs
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