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AP Statistics 3.5 Introduction to Experimental Design - MCQs - Exam Style Questions

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Question

A study of the effect of note-taking on student learning used two groups, each consisting of \(100\) biology students. On day one of the study, Group 1 was given an hour-long class on how to take notes in outline form, while Group 2 received no training. On day two, both groups were placed in a classroom, taught a lesson on biology, reviewed their notes for an hour, and then took an assessment on the lesson. Students in Group 1 performed significantly better than students in Group 2.
Which of the following statements about the study is true?
(A) The explanatory variable is the performance on the assessment.
(B) The response variable is whether training was received on taking outline notes.
(C) The experimental unit is the assessment.
(D) The treatment is the lesson on biology.
(E) A confounding variable could be whether students are good at taking assessments.
▶️ Answer/Explanation
Detailed solution
The explanatory variable is whether a student received note-taking training (training vs. no training).
The response variable is performance on the assessment (score).
The experimental unit is each student, not the assessment itself.
The lesson on biology was common to both groups, so it is not the treatment; the treatment is the training session.
A plausible confounding variable is students’ innate test-taking ability, which could affect scores regardless of training.
✅ Answer: (E)

Question

A health magazine indicated that a new supplement may reduce heartburn better than the current supplement. To investigate the claim, researchers obtained a random sample of 100 people who suffer from heartburn. After randomly assigning each person to one of two groups, the researchers gave one group the new supplement and the other group the current supplement. Of those who received the new supplement, 25 reported experiencing heartburn, and of those who received the current supplement, 35 reported experiencing heartburn.
Which of the following best describes the investigation?
(A) It was an experiment in which a treatment group was given the new supplement and a control group was given the current supplement.
(B) It was an experiment that used a matched-pairs design in which one treatment was the new supplement and the other treatment was the current supplement.
(C) It was an observational study in which the current supplement was used as a placebo to determine the effect of the new supplement at reducing heartburn.
(D) It was an observational study in which the people were observed receiving the current supplement or the new supplement.
(E) It was a census in which all 100 people participated and only the number of those who experienced heartburn was recorded.
▶️ Answer/Explanation
Detailed solution
Key features: individuals were randomly assigned to treatments (new vs current supplement) and outcomes were measured → this is an experiment with a treatment and a control group.
It is not matched pairs (no natural pairing of the same subject under both treatments).
It is not observational (the researchers imposed treatments).
✅ Answer: (A)
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