external validity

Meaning: External validity asks whether results found in one study would hold for the wider population and in real-life situations. It depends mainly on how representative the sample is of the target population and on how closely the study's setting and task resemble the real world. Ecological validity is a closely related idea that focuses on realistic settings. Tightly controlled lab experiments often gain internal validity at some cost to external validity, though the trade-off is not fixed.

On the MCAT: A passage describes a study that used college student volunteers, one culture, a small group, or a contrived lab task. The question asks what limits how far the conclusions apply, or what change would improve generalizability. Typical answers are sampling bias, nonrandom selection, a homogeneous sample, or an artificial setting. Improvements include random sampling from the target population, larger and more diverse samples, field studies, and replication with other groups.

Common confusion: Students mix up external and internal validity. Internal validity is whether the independent variable truly caused the change in the dependent variable within the study, which depends on controlling confounds and on random assignment. External validity is about generalizing, which depends on random sampling. A study can be high in one and low in the other. Neither is the same as reliability, which means consistent results on repeated measurement.