This chapter explores the principles of experimental research design as well as the issues and problems associated with different aspects of the approach. In particular, it considers the issue of internal and external validity, the common obstacles associated with experimental research, and what can be done to try and avoid or minimize them. The chapter first describes the five steps involved in the classic version of the experimental design before discussing three types of experimental design: laboratory experiments, field experiments, and natural experiments. It also examines the ethical issues that arise from experimental research and concludes by highlighting some of the advantages of experimental research.
This chapter focuses on replication and reproducibility. A single observation cannot be trusted. Similarly, findings from a single experimental investigation may reflect some regularity but they may also be due to chance, artefacts, or misinterpretations. Therefore, it is necessary to repeat the respective research procedure in order to validate the observations from the first study. Such a repetition is called replication. It is a very basic methodological tool that serves to transform an observation into a piece of validated knowledge. An observation or relationship that is found repeatedly and is also found under various scope conditions fulfils the important scientific criteria of reproducibility. There are different types of replications. The most basic distinction is between a narrow-bounded notion of replication termed direct replication and a wider notion of replication termed conceptual replication.