Which of the following claims demonstrates the strongest external validity?

• A. Heart rate increases when adrenaline production increases.
• B. The age at which a child first walks is a predictor of their level of extraversion.
• C. Men are better at professions requiring mathematics and engineering skills.
• D. Women provide more food calories in hunter-gatherer societies.

Answer: (B)

External validity is about whether findings generalize beyond the specific people, places, times, or conditions in which a study was conducted. The claim that the age at which a child first walks predicts their level of extraversion best illustrates this kind of generalization. It suggests a developmental pattern that could apply across different children and settings, not just within a single experiment or sample, implying the result could hold across various populations and contexts.

The other statements rely on mechanisms or generalizations that are harder to extend beyond the original context. A relation between heart rate and adrenaline is a physiological link often demonstrated under controlled conditions, which limits broad generalization. Broad assertions about group differences—such as men being better at mathematics and engineering, or women providing more calories in hunter-gatherer societies—tend to reflect cultural, contextual, or sample-specific factors and don’t guarantee applicability to other groups or settings.