experimental design makes up for the shortcomings of
the two designs previously discussed.
They employ both a control group and a means
to measure the change that occurs in both groups.
In this sense, we attempt to control for all
confounding variables, or at least consider their
impact, while attempting to determine if the
treatment is what truly caused the change.
The true experiment is often thought of as
the only research method that can adequately measure
the cause and effect relationship.
Below are some examples:
Equivalent Groups Study.
Randomization and the comparison of both a
control and an experimental group are utilized in
this type of study. Each
group, chosen and assigned at random is presented
with either the treatment or some type of control.
Posttests are then given to each subject to
determine if a difference between the two groups
this is approaching the best method, it falls short
in its lack of a pretest measure. It is difficult to determine if the difference apparent at
the end of the study is an actual change from the
possible difference at the beginning of the study.
In other words, randomization does well to
mix subjects but it does not completely assure us
that this mix is truly creating an equivalency
between the two groups.
Posttest Equivalent Groups Study.
Of those discussed, this method is the most
effective in terms of demonstrating cause and effect
but it is also the most difficult to perform.
The pretest posttest equivalent groups design
provides for both a control group and a measure of
change but also adds a pretest to assess any differences
between the groups prior to the study taking place.
To apply this design to our work experience
study, we would select students from the college at
random and then place the chosen students into one
of two groups using random assignment.
We would then measure the previous semesters
grades for each group to get a mean grade point average.
The treatment, or work experience would be
applied to one group and a control would be applied
to the other.
is important that the two groups be treated in a
similar manner to control for variables such as
socialization, so we may allow our control group to
participate in some activity such as a softball
league while the other group is participating in the
work experience program.
At the end of the semester, the experiment
would end and the next semesters grades would be
gathered and compared.
If we found that the change in grades for the
experimental group was significantly different than
the change in the grades of our control group, we
could reasonably argue that one semester of work
experience compared to one semester of non-work
related activity results in a significant difference
5.3: Diagrams of True Experimental Designs