P = The general population
U = An unrandomized group
O1 = The pre-intervention observation
X = The intervention (the independent variable)
O2 = The the post-intervention observation (the dependent variable)

Type:

Pre-experimental Research Design

What it is:

The single group pre-post design is similar to the single shot study but adds an additional observation before the intervention to provide a control for comparison. In this design, an unrandomized group is arbitrarily selected from the general population, observed, and the data recorded. An intervention is administered and then the results are observed and recorded.

Method:

Step One

Choose an arbitrary group from the general population "P" and designate this group as the experimental group "U".

Step Two

Observe and record pre-intervention characteristics of interest "O1" of the experimental group "U".

Step Three

Administer the intervention "X" to the experimental group "U".

Step Four

Observe and record the outcome of the interaction "O2" on the experimental group "U".

Step Five

Summarize, analyze, and report the results.

Threats to Validity

History

Lack of control introduces history threat potentially worse than the one shot study.

Maturation

Lack of control introduces maturation threat potentially worse than the one shot study.

Testing Effects

Administration of first test can affect outcome of second test.

Instrumentation

Probably negligible. Depends on the method selected.

Statistical Regression

Multiple testing introduces regression effects.

Selection

Makeup of unrandomized group capable of effecting results.

Attrition

The pretest provides greater control thus reducing attrition affects compared with a Type I study.

Interaction

Must always be considered.

Remarks:

The observations could be in the nature of tests or surveys and the like.  For example, "O1" could be a survey about attitudes about the war, the intervention "X" could be watching a graphic war movie and "O2" could be a readministration of the survey to test for change in attitude about the war. Note, however, that adding the extra step aggravates existing threats or introduces additional threats compared with the Type I method.

—By Douglas E. Greathouse, MA. (2007)