External validity is a term used in scientific research. It signifies the extent to which the results of a study can be applied to circumstances outside the specific setting in which the research was carried out. In other words, it addresses the question "Can this research be applied to 'the real world'?"

External validity is also known as the 'generalizability' of a study. In other words, "Can I generalize the results of this study to the population I am investigating?"

In assessing the external validity of a study, it is helpful to evaluate threats and strengths. Examine the population in which the study is performed. Look at the age, race, geographic location and other demographic variables to decide whether the results of the study can apply to the population you are investigating.

Other types of validity

There are numerous types of validity, like concurrent-, content-, convergent-, criterion-, discriminant-, face-, or predictive validity. Within this framework, four types of validity are playing an essential role in causal inference. External validity is one of them. The other three are internal validity, statistical-conclusion validity and construct validity. Internal validity is a term pertaining to scientific research that signifies the extent to which the conditions within a research design were conducive to drawing the conclusions the researcher was interested in drawing. ... In statistics a valid measure is one which is measuring what it is supposed to measure. ... In social science and psychometrics, construct validity refers to whether a scale measures the unobservable social construct (such as fluid intelligence) that it purports to measure. ...