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GMAT Tips: Breaking Down a GMATPrep CR Explain a Discrepancy Problem

Today’s GMAT tip comes from test prep firm ManhattanGMAT. In this article, they provide helpful tips for how to identify and answer “explain a discrepancy” questions in the Critical Reasoning section of the GMAT.  Read on to see what they have to say!

This week, we’re going to tackle a harder GMATPrep critical reasoning question from the Explain A Discrepancy category.

Let’s start with the problem. Set your timer for 2 minutes!

* “According to a review of 61 studies of patients suffering from severely debilitating depression, a large majority of the patients reported that missing a night’s sleep immediately lifted their depression. Yet sleep-deprivation is not used to treat depression even though the conventional treatments, which use drugs and electric shocks, often have serious side effects.

“Which of the following, if true, best explains the fact that sleep-deprivation is not used as a treatment for depression?

“(A) For a small percentage of depressed patients, missing a night’s sleep induces a temporary sense of euphoria.

“(B) Keeping depressed patients awake is more difficult than keeping awake people who are not depressed.

“(C) Prolonged loss of sleep can lead to temporary impairment of judgment comparable to that induced by consuming several ounces of alcohol.

“(D) The dramatic shifts in mood connected with sleep and wakefulness have not been traced to particular changes in brain chemistry.

“(E) Depression returns in full force as soon as the patient sleeps for even a few minutes.”

Okay, now that you’ve got an answer, we’re going to go back to the question stem and argument and forget about the answers for a moment. How do you identify the question type? What should you know about that question type before you even start to read the argument? What should you look for in the argument? What might your notes have looked like?

Reading the Question and Argument

First, if you haven’t already, you may want to take a look at this article: Strategies for Critical Reasoning.

As the article says, we read the question stem first. This is the question stem:

“Which of the following, if true, best explains the fact that sleep-deprivation is not used as a treatment for depression?”

The key identifying language is “explain the fact that <something unexpected is true or is happening>.” This language reflects an Explain A Situation or Explain A Discrepancy problem type.

What kind of information is found in Explain A Discrepancy questions and what are we supposed to do with that information?

Explain questions typically have only premises, no conclusion, and the premises tend to be more fact-based than opinion-based. Typically, two sets of facts will be presented and those facts will appear contradictory in some way. They may even give us a clue in the form of contrast language: yet, though, however, surprisingly, and so on. My first task is to separate the two contradictory pieces of information: X is true BUT (surprisingly) Y is also true at the same time.

In this argument, the first sentence presents some information. The second sentence begins with the word “yet” (a contrast marker!) and then provides seemingly contradictory information. I might put that down on my scrap paper in this form:

lg maj P: no slp 1 night à less deprBUT we don’t treat depr by losing slp 

even tho normal trtmnt = bad side eff

 

What does this mean in normal, non-GMAT language? Most depressed patients feel better if they miss a night of sleep, yet doctors don’t actually use this as a treatment option. Even more simply: there’s this thing that seems like it would be useful, but doctors don’t actually use it.

Why?

That’s really the question we’re trying to answer. Right now, the information is puzzling. If it’s the case that missing some sleep leads to such a strong benefit, then why wouldn’t doctors want to take advantage of that? The correct answer will explain why, and when we combine the correct answer with the original argument, we should think: Oh, it actually makes sense now why the doctors wouldn’t do that!

Okay, now we know what we need to do. There’s just one more thing: the trap wrong answers for this question type.

On Explain questions, the most tempting traps are often “opposite” traps: answers that explain that there is a discrepancy, or emphasize the discrepancy. Our job is not to show that the discrepancy exists or to explain what it is; our task is to show that there really isn’t a discrepancy at all. Keep this in mind and you will be a lot less likely to fall into an “opposite” trap.

Answering the Question

To recap: we’re looking for a reason that explains why the doctors don’t want to use a treatment (sleep deprivation) that seems to be good for depressed patients. The most obvious thing I can think of right now: there’s some additional effect or effects that are negative. I have to keep in mind, though, that the right answer could address something else that hasn’t occurred to me.

Now, go through the answers and eliminate any that you think are definitely wrong. For any that might be right, don’t eliminate yet; save them for a later comparison.

Answer A discusses depressed patients – that’s good because it’s within the scope of the argument – and says that some feel “euphoria” after missing a night’s sleep. Euphoria means to feel elated, or extremely happy. That’s a good thing; maybe that explains why the patients’ depression lifts. It doesn’t explain the other half though: why doctors don’t use sleep deprivation as a treatment. Eliminate A.

Answer B compares depressed patients to patients who are not depressed. That’s starting to get a little bit out of scope. The information conveyed in the comparison is also potentially tempting but ultimately irrelevant to the question of why doctors don’t employ sleep deprivation. It’s tempting because perhaps it’s next to impossible to keep depressed patients awake, or it would cost $100,000 per person per night to keep a depressed patient awake. It doesn’t say that it’s very hard to keep depressed patients awake, though, does it? It only says that it’s harder than keeping awake those who are not depressed. Perhaps it’s extremely easy to keep non-depressed patients awake and only slightly harder to keep depressed patients awake. Eliminate B.

Answer C looks pretty good. If we deprive the depressed patients of sleep, then something bad happens: their judgment is impaired. Leave this one in for now.

Answer D says that we don’t know exactly what’s going on in the brain when our moods shift. But doctors don’t need to know why a treatment works, necessarily – they just need to know that the treatment is beneficial. This one doesn’t tell us that the treatment is less beneficial, only that we don’t know quite how it actually works. Eliminate D.

Answer E looks pretty good, too. This one’s telling us that maybe the treatment just isn’t worth it. Obviously, we can only keep people awake for so long; then, they have to sleep. And, as soon as they sleep even a little bit, they lose all of the benefits… so why bother?

A, B, and D are out. We need to examine C and E again. Often, at this stage, the distinction will hinge upon language that goes too far beyond the scope of the argument. Does either answer make an assumption about something or go too far beyond what’s specifically described in the argument?

Hmm. C uses the word “prolonged.” Prolonged loss of sleep… that doesn’t really fit the argument. The argument talked about missing just one night of sleep – that isn’t “prolonged.” If we can get the benefit after just one night of missing sleep, then we don’t have to deprive the patients of sleep for a prolonged period of time. So this negative effect may not actually apply in this case – and it doesn’t explain why the doctors wouldn’t at least try having patients skip just one night of sleep.

E, on the other hand, mentions that the depression comes back completely after sleeping for only a few minutes. So I can miss one night of sleep and get a lift, but as soon as I sleep the next night (or nap during the day, since I didn’t sleep at all the night before!), I lose the entire benefit. If that’s true (and the question stem told us to assume that it is!), then it makes sense that doctors wouldn’t bother to try depriving patients of even a single night’s sleep.

The correct answer is E.

Key Takeaways for Solving Explain A Discrepancy CR Problems:

(1) Know how to recognize this type. Explain A Situation or Explain A Discrepancy questions will often contain language such as “explain the fact that” or similar.

(2) Know what to do with Explain questions. Your first task is to find the discrepancy itself. Then, ask yourself why this would be true; if you can think of any possible explanations that would show there isn’t a discrepancy after all, jot down a note on your scrap paper. Finally, go look for an answer that, when added to the argument, results in someone saying, “Oh, that makes sense! There isn’t actually a discrepancy after all!”

(3) Know what you’re not trying to do as well. We’re not trying to prove that there is a discrepancy or explain what the discrepancy is.

* GMATPrep questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

For more information on ManhattanGMAT, download Clear Admit’s independent guide to the leading test preparation companies here. This FREE guide includes coupons for discounts on test prep services at ten different firms!

Posted in: GMAT - Verbal, GMAT Tips

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