External validity concerns generalizing findings to real-world settings. Which option describes a threat to external validity?

• A. Nonrepresentative samples.
• B. Large, representative samples.
• C. Realistic, ecologically valid tasks.
• D. Consistent replication across settings.

Answer: (A)

External validity means whether findings would apply beyond the study to real-world settings and other populations. A threat to external validity occurs when the sample studied doesn't reflect the population you want to generalize to, so the results may not hold in other groups or contexts. Nonrepresentative samples can lead to biased conclusions that don’t transfer outside the study, like testing an intervention only in a narrow group (such as college students) and assuming the same effects would occur in all adults. In contrast, large, representative samples improve generalizability; realistic, ecologically valid tasks ensure the observed behavior mirrors real-life situations; and consistent replication across settings shows the results hold across different contexts. So, nonrepresentative samples are the clear threat to external validity.