ABSTRACT
External validity is the extent to which research results can be applied outside the specific context in which the data were collected. The generalizability aspect of external validity is the extent to which research results can be replicated under new conditions. The ecological validity or naturalism of research addresses whether theories or sets of findings can be applied to specific natural situations. External validity can be affected by structural factors, including characteristics of the physical setting, reactivity, researcher attributes, and co-participant attributes, and can be affected by culture and changes in social norms over time. The functional component of external validity concerns the similarity of the psychological processes that affect behavior in the natural and research settings. The conceptual component of external validity is the degree to which the problem studied in the research situation corresponds to a problem found in a natural setting. The chapter describes ways of assessing external validity and covers the continuing controversy over whether laboratory research results apply to natural settings. The relationship between internal validity and external validity is discussed.
