The elementary quasi-experimental design known as the before-after design involves the measurement of "outcome" indicators (e.g., arrest rates, attitudes) prior to implementation of the treatment, and subsequent re-measurement after implementation. Any change in the measure is attributed to the treatment. This design provides a significant improvement over the one-shot study because it measures change in the factor(s) to be impacted. However, this design suffers from threats of history - the possibility that some alternate factor (besides the treatment) has actually caused the change.
US Environmental Protection Agency. (2007). Program Evaluation Glossary. Office of the Administrator/Office of Policy/Office of Strategic Environmental Management/Evaluation Support Division.