Chapter 6: Research Strategies and Validity

The chapter establishes precise definitions of research strategy, research design, and research procedure, clarifying the hierarchical decisions and structural frameworks that guide study development from conception to implementation. A central focus involves distinguishing between internal validity, which concerns whether observed effects result from the independent variable rather than alternative explanations, and external validity, which addresses the generalizability of findings to populations and contexts beyond the immediate study. The chapter systematically catalogs threats to internal validity, including selection bias, volunteer bias, sensitization effects, participant variables, and confounding variables that can obscure causal relationships. Environmental, temporal, and participant-related factors that compromise validity are examined alongside artifacts such as experimenter bias, demand characteristics, and participant reactivity that can systematically distort research outcomes. The chapter emphasizes the critical tension between internal and external validity, demonstrating that maximizing experimental control to isolate causal mechanisms often reduces the real-world applicability of results, while increasing ecological realism may introduce uncontrolled variables. Through illustrative examples and comparative analysis, the chapter equips students with frameworks for evaluating research quality, recognizing validity threats in published studies, and making informed methodological choices that align with specific research goals and constraints.