Breaking Down a GMATPrep CR Explain A Discrepancy Problem
This week, were going to tackle a harder GMATPrep critical reasoning question from the Explain A Discrepancy category.
Lets 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 nights 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 nights 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 youve got an answer, were 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 havent 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 this down on my scrap paper.
| P: no slp 1 night less depr | BUT we dont treat depr by 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 dont actually use this as a treatment option. Even more simply: theres this thing that seems like it would be useful, but doctors dont actually use it.
Why?
Thats really the question were trying to answer. Right now, the information is puzzling. If its the case that missing some sleep leads to such a strong benefit, then why wouldnt 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 wouldnt do that!
Okay, now we know what we need to do. Theres 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 isnt 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: were looking for a reason that explains why the doctors dont 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: theres some additional effect or effects that are negative. I have to keep in mind, though, that the right answer could address something else that hasnt occurred to me.
Now, go through the answers and eliminate any that you think are definitely wrong. For any that might be right, dont eliminate yet; save them for a later comparison.
Answer A discusses depressed patients thats good because its within the scope of the argument and says that some feel euphoria after missing a nights sleep. Euphoria means to feel elated, or extremely happy. Thats a good thing; maybe that explains why the patients depression lifts. It doesnt explain the other half though: why doctors dont use sleep deprivation as a treatment. Eliminate A.
Answer B compares depressed patients to patients who are not depressed. Thats 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 dont employ sleep deprivation. Its tempting because perhaps its 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 doesnt say that its very hard to keep depressed patients awake, though, does it? It only says that its harder than keeping awake those who are not depressed. Perhaps its 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 dont know exactly whats going on in the brain when our moods shift. But doctors dont need to know why a treatment works, necessarily they just need to know that the treatment is beneficial. This one doesnt tell us that the treatment is less beneficial, only that we dont know quite how it actually works. Eliminate D.
Answer E looks pretty good, too. This ones telling us that maybe the treatment just isnt 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 whats specifically described in the argument?
Hmm. C uses the word prolonged. Prolonged loss of sleep that doesnt really fit the argument. The argument talked about missing just one night of sleep that isnt prolonged. If we can get the benefit after just one night of missing sleep, then we dont 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 doesnt explain why the doctors wouldnt 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 didnt sleep at all the night before!), I lose the entire benefit. If thats true (and the question stem told us to assume that it is!), then it makes sense that doctors wouldnt bother to try depriving patients of even a single nights sleep.
The correct answer is E.
Key Takeaways for Solving CR Explain A Discrepancy Problem:
(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 isnt 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 isnt actually a discrepancy after all!
(3) Know what youre not trying to do as well. Were 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.