Laboratory experiments are the type of study that most people have in mind when talking about experiments. In this chapter, we first discuss the strengths of laboratory experiments, which offer the highest degree of experimental control as compared to other types of experiments. Single factors can be manipulated according to the requirements of theories under highly controlled conditions. As such, laboratory experiments are well-placed to test theories. We then introduce a sociological laboratory experiment as a leading example, which we use as a reference for a discussion of several principles of laboratory research. Furthermore, we discuss a second goal of laboratory experiments, which is the establishment of empirical regularities in situations where theory does not provide sufficient guidance for deriving behavioral expectations. The chapter concludes with a short discussion of caveats for the analysis of sociological data generated in laboratory experiments.

This chapter addresses the often-misunderstood concept of validity. Much of the methodological discussion around sociological experiments is framed in terms of internal and external validity. The standard view is that the more we ensure that the experimental treatment is isolated from potential confounds (internal validity), the more unlikely it is that the experimental results can be representative of phenomena of the outside world (external validity). However, other accounts describe internal validity as a prerequisite of external validity: Unless we ensure internal validity of an experiment, little can be said of the outside world. We contend in this chapter that problems of either external or internal validity do not necessarily depend on the artificiality of experimental settings or on the laboratory–field distinction between experimental designs. We discuss the internal–external distinction and propose instead a list of potential threats to the validity of experiments that includes "usual suspects" like selection, history, attrition, and experimenter demand effects and elaborate on how these threats can be productively handled in experimental work. Moreover, in light of the different types of experiments, we also discuss the strengths and weaknesses of each regarding threats to internal and external validity.