is the validity of generalized (causal) inferences in scientific studies, usually based on experiments as experimental validity
.Mitchell, M. & Jolley, J. (2001). Research Design Explained (4th Ed)
Inferences about cause-effect relationships based on a specific scientific study are said to possess external validity if they may be generalized from the unique and idiosyncratic settings, procedures and participants to other populations and conditions.Brewer, M. (2000). Research Design and Issues of Validity. In Reis, H. & Judd, C. (eds) Handbook of Research Methods in Social and Personality Psychology.
Cambridge:Cambridge University Press.Shadish, W., Cook, T., & Campbell, D. (2002). Experimental and Quasi-Experimental Designs for Generalized Causal Inference
Boston:Houghton Mifflin. Causal inferences said to possess high degrees of external validity can reasonably be expected to apply (a) to the target population of the study (i.e. from which the sample was drawn) (also referred to as population validity), and (b) to the universe of other populations (e.g. across time and space).
The most common loss of external validity comes from the fact that experiments using human participants often employ small samples obtained from a single geographic location or with idiosyncratic features (e.g. volunteers). Because of this, one cannot be sure that the conclusions drawn... Read More