ABSTRACT
This chapter discusses on the difference between a genuine experimental design and a quasi-experimental design. It also discusses on how the addition of a control group improves a time series design. The chapter examines how the addition of a pretest improves a nonequivalent group, posttest-only design. Most research projects in advertising and public relations do not have sufficient time, money, or inclination to include longitudinal designs. The interrupted time series design allows for researchers to examine some key variable over time. At the most basic level, the interrupted time series design is an experimental-group-only quasi-experiment with multiple pretests and multiple posttests. Quasi-experiments can provide meaningful insight if conducted correctly. However, interpretation of data must always be in light of the lack of true randomization. Quasi-experiments can hint at causation, but they cannot assure it. One must be careful not to draw rigid conclusions based upon quasi-experiments.
