Population of interest is adolescents 13-15 in the United States. The researcher recruits 50 participants from a local junior high school and manipulates peers on learning tasks. The researcher holds other variables constant. This minimizes which and maximizes which?

• A. Internal validity to maximize population validity.
• B. Population validity to maximize internal validity.
• C. Both external validity and population validity.
• D. Population validity to maximize external validity.

Answer: (B)

The main idea here is how experimental control and sampling affect internal validity versus population (external) validity. Holding other variables constant helps ensure that any observed effect on learning tasks is due to the manipulated peer condition, not something else. This strengthens internal validity by reducing alternative explanations.

At the same time, recruiting participants from only one local junior high school limits how well the findings generalize to all US adolescents aged 13–15, which weakens population validity.

So this setup increases internal validity while reducing population validity. The best description is that population validity is minimized while internal validity is maximized.