A researcher wants to test whether listening to music while studying improves memory recall. She recruits 80 students from a dormitory. She pairs students by similar GPA, then within each pair randomly assigns one student to study vocabulary words for 20 minutes with instrumental music and the other to study in silence. Afterward, both take the same recall quiz. Which conclusion is justified based on the design?
- Because students were paired and randomly assigned within pairs, a cause-and-effect conclusion about music and recall is justified for these 80 students. (correct answer)
- Because students were paired, the results can be generalized to all college students.
- Because students were not randomly sampled, the study cannot show whether music affects recall even for the dormitory students.
- Because this is a matched-pairs observational study, only association can be concluded.
- Because the researcher recruited volunteers, random assignment is invalid and causation cannot be concluded.
Explanation: This question assesses AP Statistics matched-pairs experimental design and its inferential power. Pairing by GPA and random assignment within pairs to music or silence enables a cause-and-effect conclusion about recall for these 80 students, as it controls for ability confounders. Recruiting from a dormitory without random sampling limits generalization beyond these volunteers, not to all college students. Choice D is a distractor, mislabeling it as observational despite assignment. A mini-lesson on inference: matched-pairs experiments with random assignment strengthen causality by reducing variability; sampling is for broader application. Thus, causation is justified for the recruited students.