Q21 - In an experiment, some volunteers were assigned

[Laura Damone]

Question Type:
Necessary Assumption

Stimulus Breakdown:
Conclusion: the experiment provides good evidence that aerobic exercise helps the body handle stress. Premises: the experiment had some folks do aerobics and others weight train. After three months of classes, everyone did a hard math problem. After the math problem, the aerobics group had fewer measurable stress symptoms than the weight trainers.

Answer Anticipation:
There's a lot of gaps in this reasoning, which makes it hard to come up with a single prephrase. But since there isn't a big term shift, we should predict that the right answer will probably be a Defender Assumption that mitigates a potential objection. We should also note that this argument is comparative and be on the look out for wrong answers that make irrelevant comparisons.

Correct answer:
E

Answer choice analysis:
(A) Out of scope. We don't need the body to fully benefit from the aerobics. We just need there to be the psychological benefit of handling stress better.

(B) The argument in the stimulus compares two groups, the aerobics group and the weight training group, and concludes that doing aerobics accounts for the difference in their stress levels after the math problem. In order for that argument to work, only one group can be doing aerobics. But it's ok if both are lifting weights. B is very tempting for this reason, but the negation test can help you rule it out. If some of the aerobics group are lifting weights too, so what? It doesn't blow up the argument that the aerobics is the cause of their lower stress.

(C) Total amount of exercise before vs. during the experiment is an irrelevant comparison.

(D) This one is tempting, especially if you anticipated an answer that deals with the relationship between performance and stress. For example, perhaps aerobics makes you better at math, so the reduced stress symptoms in the aerobics group is because the problem felt easy, not because aerobics helps them process stress. But that's an objection to the argument, not an assumption of the argument. The assumption is the inverse: the aerobics group didn't find the math problem easier. That means C is the opposite of what we need. If you were tempted by this one, the negation test will help you rule it out. The negation here would support the argument, not destroy it.

(E) In order to reach our conclusion that the aerobics caused the aerobics group to have lower stress, we need them to be getting more aerobic exercise than the weight training group. If you're unsure about this answer, negate it! If the weight training group got more aerobic exercise, the argument falls apart.

Takeaway/Pattern:
When comparative arguments establish that two things are different in one respect, then concludes that the first difference is the cause for some second difference, you need to make sure that the first difference is definite and that it is the only relevant difference that could account for the second difference. But, if that sounds like an overly-ambitious prephrase, simply noting the comparative nature of the argument, looking out for irrelevant comparisons and scope issues, and working wrong to right with the negation test at the ready should still get you to the right answer.

#officialexplanation

[DavidH327]

I chose B by overlooking difference between "lifting weights outside the classes"(this answer choice) vs "taking weight-training classes." (stimulus says)

If the answer choice was worded so that
volunteers who were assigned to aerobics class did not also take weight-training class, it would be a necessary assumption right?
Because if there were overlaps in training, it could have been weight-training that might helped body to handle stress instead of aerobics classes.

[ohthatpatrick]

Not quite.

Say that people A, B, C, D all took aerobics AND weight training classes.
People W, X, Y, Z just took the weight training class.

If we do this whole math challenge later and find out that the stress levels of A, B, C, D were lower than those of W, X, Y, Z,
would it be a plausible hypothesis to say that the WEIGHT TRAINING classes are what lowered the stress levels of A, B, C, D?

It wouldn't because both groups of people had weight training classes. If that were really the cause of the lower stress levels, then both groups would have lower stress levels.

What Laura was saying is that if we found out that "the volunteers assigned to weight classes ALSO did aerobics", that would weaken the argument. If both groups did aerobics to a similar degree, then aerobics couldn't be the causal explanation for the DISSIMILARITY between the groups when it came to stress levels.

The supposed causal difference maker (aerobics) should be unique to the group who had the observed effect.

The supposed non-factor (weights) can be shared or unique; it doesn't affect the logic either way.

[LinC521]

@ohthatpatrick

I think B is necessary because if the group who are assigned aerobic exercises also do lift weighting, then the difference becomes the volume of their doing exercises. I.e. the first group do more exercise than the group 2.
The handling of stress can be explained by doing more exercises instead of doing aerobic exercise.

[LinC521]

Not quite.

Say that people A, B, C, D all took aerobics AND weight training classes.
People W, X, Y, Z just took the weight training class.

If we do this whole math challenge later and find out that the stress levels of A, B, C, D were lower than those of W, X, Y, Z,
would it be a plausible hypothesis to say that the WEIGHT TRAINING classes are what lowered the stress levels of A, B, C, D?

It wouldn't because both groups of people had weight training classes. If that were really the cause of the lower stress levels, then both groups would have lower stress levels.

What Laura was saying is that if we found out that "the volunteers assigned to weight classes ALSO did aerobics", that would weaken the argument. If both groups did aerobics to a similar degree, then aerobics couldn't be the causal explanation for the DISSIMILARITY between the groups when it came to stress levels.

The supposed causal difference maker (aerobics) should be unique to the group who had the observed effect.

The supposed non-factor (weights) can be shared or unique; it doesn't affect the logic either way.

@ohthatpatrick

I think B is necessary because if the group who are assigned aerobic exercises also do lift weighting, then the difference becomes the volume of their doing exercises. I.e. the first group do more exercise than the group 2.
The handling of stress can be explained by doing more exercises instead of doing aerobic exercise.

[HenryC546]

I’m neither a native English speaker nor a gym rat, so it’s hard for me to intuit that aerobics and weight-training overlap (I actually thought the former was something related to acrobatics and I just treated them as two different kinds of exercises, like running and swimming). Even so, I still find it strange that we should’ve assumed about the overlap—that weight-training involves some aerobics (and vice versa?)—since they are introduced as two separate things and we’re supposed to be alert to any concept shift.

Now knowing the overlap, I can see why E is correct, but I still can’t eliminate B, because what if neither aerobics nor weight-training can single-handedly help the body handle psychological stress? What if it’s “aerobics classes + weight lifting” that help? One has to do them both to handle psychological stress. I think B addresses that as a defender answer, eliminating a potential cause. I know it sounds ridiculous but in assumption question, defender answer usually sounds ridiculous, doesn't it?