After reading this chapter, you should be able to:

9.1 Understand the difference between the three main types of quantitative research designs (randomized experimental, quasi-experimental, and observational) and evaluate their internal and external validity.

9.2 Understand the distinctions between posttest-only, repeatedmeasurement, and multigroup experimental designs.

9.3 Discuss the use of field experiments and natural experiments in political science research and understand how they differ from laboratory experiments.

9.4 Describe the quasi-experimental design and its limitations.

9.5 Describe two types of observational research designs—cross-sectional designs and longitudinal designs—and explain how they contribute to our understanding of political phenomena.