External validity is best understood as the study’s generalizability to the broader population, contingent upon which prerequisite?

• A. Internal validity is present and credible.
• B. Large sample size guarantees generalizability.
• C. No biases exist in measurement.
• D. Participants are tested under the exact same conditions as usual practice.

Answer: (A)

External validity is about whether study findings generalize to broader populations and settings. The prerequisite for that generalizability is that internal validity is present and credible. When internal validity is solid, the observed effect is more likely to reflect a true relationship rather than bias or confounding, making generalization to similar populations and real-world contexts reasonable. If internal validity is compromised, biases or measurement errors can distort the results, undermining any claim of generalizability. A large sample size helps precision but does not by itself guarantee generalizability, and matching testing conditions to usual practice relates to realism but isn’t the core prerequisite for external validity.