PrepTest 151, Section 3, Question 21

What we’re looking for

Working the answers

• A

  Full benefit is unnecessary. Even a partial benefit could support the claim that aerobic exercise helps the body handle stress. The author doesn't need three months to deliver everything aerobic exercise could possibly offer.

• B

  This is tempting because exercise outside the assigned classes could complicate the study. But the argument doesn't need the aerobics group to avoid every bit of weightlifting. For example, both groups might lift the same amount overall while differing in their aerobic exercise. Outside weightlifting wouldn't automatically destroy the comparison.

  The conclusion also doesn't claim aerobics is better than weightlifting. Still, we shouldn't dismiss all comparisons on that basis: the evidence does compare two groups. The question is which difference between them the author needs, not whether every other kind of exercise must be absent.

• C

  More exercise overall isn't the same as more aerobic exercise. Someone could replace an hour of another activity with an hour of aerobics without increasing total exercise. Also, the evidence compares the two groups after the experiment, not each person's stress before and after an increase in total exercise. C isn't required for that evidence to support the conclusion.

• D

  Finding the calculation easier isn't required for handling its stress better. Someone might find a problem extremely difficult and remain calm while working on it. The conclusion concerns the body's response to psychological stress, not an improvement in mathematical ability or a reduction in perceived difficulty.

• E
  Correct

  This reaches a different issue from my initial concerns: being assigned to an aerobics class doesn't necessarily mean getting more aerobic exercise overall.

  At first, a comparison with the weight-training group might seem unnecessary because the conclusion isn't that aerobics beats weightlifting. But look back at the evidence: the aerobics class had fewer stress symptoms than the other class. To use that difference as evidence for the benefit of aerobic exercise, the author needs the aerobics group actually to have done more of it.

  Suppose the weight-training volunteers also ran every day outside class, while the aerobics volunteers did no additional aerobic exercise. The class labels could then hide equal amounts of aerobic exercise, or even more in the weight-training group. In that case, the lower stress in the aerobics class wouldn't show the benefit of getting more aerobic exercise. E supplies the needed difference in actual activity, including what happened outside class. It doesn't resolve every concern about the experiment, but this comparison needs it.