Every research study is conducted at a specifi c time and place with specifi c
participants, instructions, measurement techniques, and procedures. Despite
the unique nature of the study itself, researchers usually assume that the
obtained results are not unique but can be generalized beyond that study.
External validity concerns the extent to which the results obtained in a
research study hold true outside that specifi c study. Can the results of the
study be generalized to other populations, other settings, or other measurements?
For example, Strack, Martin, and Stepper (1988) conducted a study
showing that people rate cartoons as funnier when holding a pen in their teeth
(which forced them to smile) than when holding a pen in their lips (which
forced them to frown). Although this study was done in 1988 using undergraduate
students from the University of Illinois, it seems reasonable to assume
that the results are still valid today. That is, if the same study were conducted
with today’s undergraduate students from a different university, it
would be reasonable to expect essentially the same results.
External validity focuses on any unique characteristics of the study that
may raise questions about whether the same results would be obtained under
different conditions. Any factor that limits the ability to generalize the results
from a research study is a threat to external validity. For example, the results
obtained from a group of 50-year-old males do not necessarily generalize
to females or to other age groups. In this case, the limited range of participant
characteristics is a threat to the external validity of the study.