Chapter 9 – Evaluating Experimental Procedures

Experiments are different from all other study types in social sciences in that they test the effects of “treatment” on outcomes. The most rigorous testing of cause-and-effect relationships involves true experiments or randomized controlled trials that include the random assignment of participants to the experimental and control groups. This chapter includes evaluation questions and examples organized into six major categories: (1) Composition of the experimental and control groups, (2) Similarity of treatment and control conditions from the participants’ perspective, (3) Sufficient numbers of participants, (4) How outcomes of the experiment were evaluated, (5) Considerations for quasi-experiments, and (6) Treatment details. The key characteristics of the experimental procedures are discussed, with special attention to what constitutes blind and double-blind experiments, demand characteristics, cross-group contamination, treatment compliance, history effect, how the random assignment of individuals to treatments differs from the random assignment of groups to treatments, and how attrition can affect the results of experiments. This chapter highlights the issues of internal and external validity in true and quasi-experiments as well as the differences between random assignment and random selection. The exercises at the end of the chapter reinforce the application of the knowledge gained.