Causation question : GMAT Verbal Section
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# Causation question

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06 Apr 2008, 11:01
Can somebody please be so kind as to explain me why the ans is E and not D (example comes from Kaplan's GMAT 800 - but I still don't get the explanation).

Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools.

Which of the following, if true, most seriously weakens the argument above?

A. The high school system in Gotham succeeds in giving students a good education at considerably less cost than do most systems.

B. Several cities have found that overcrowding in the schools is not always associated with lower reading scores.

C. Gotham schools have a greater teacher-to-student ratio than most other school systems.

D. Students' reading skills have not declined in other cities where the high schools are just as overcrowded as those of Gotham.

E. Schools are not overcrowded in many cities where high school reading scores have declined more than they have in Gotham.

Why E??? For me it's clearly D because:
1) it offers alternative explanation (there must be some other reason for decline in reading skills than overcrowded schools)
2) E talks about "scores" not "skills" - isn't it a shift of scope?
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06 Apr 2008, 11:41
garbus222 wrote:
Can somebody please be so kind as to explain me why the ans is E and not D (example comes from Kaplan's GMAT 800 - but I still don't get the explanation).

Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools.

Which of the following, if true, most seriously weakens the argument above?

A. The high school system in Gotham succeeds in giving students a good education at considerably less cost than do most systems.

B. Several cities have found that overcrowding in the schools is not always associated with lower reading scores.

C. Gotham schools have a greater teacher-to-student ratio than most other school systems.

D. Students' reading skills have not declined in other cities where the high schools are just as overcrowded as those of Gotham.

E. Schools are not overcrowded in many cities where high school reading scores have declined more than they have in Gotham.

Why E??? For me it's clearly D because:
1) it offers alternative explanation (there must be some other reason for decline in reading skills than overcrowded schools)
2) E talks about "scores" not "skills" - isn't it a shift of scope?

Here is why it is not D --

It is possible that the schools in Gotham have now become equally overcrowded as the schools in other cities while that was not the case before. Where as the schools in the other cities have not seen any increase in the overcrowding and hence the students' reading skills have not declined.

For example in 1985:
Gotham City overcrowding ratio = 0.85, Other Cities overcrowding ratio = 0.99
Reading Skill for Gotham City Students = 87, Reading Skill for Other city students = 75

Now in 1989:
Gotham City overcrowding ratio = 0.99, Other Cities overcrowding ratio = 0.99 (unchanged)
Reading Skill for Gotham City Students = 75, Reading Skill for Other city students = 75

So just the fact that the students of other cities have not seen any declines in reading skills (even though the crowding ratio is equal) is not enough to weaken the argument.

E makes sense....think it through...
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06 Apr 2008, 13:17
If I didn't read E, I would probably picked D.

But E is right, the problem is "the problem can only be caused by overcrowding" is the argument. To weaken this argument, the best counter is to say there are other school with different set of situation are experiencing the same problem they have, thus there are other causes for the problem and overcrowding isn't the only one. If the problem states this way: "The problem is caused by overcrowding" then D would be the right answer. See the difference?

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07 Apr 2008, 11:31
Neelesh, Billyjeans - thanks for replies. Neelesh - thank you for explanation and very useful example illustrating the issue!
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07 Apr 2008, 12:31
A -irrelevant
B-sounds good
C-not sufficient
D- strengthen the arg , so false
E-means over crowding is NOT the cause ..nails it!

now, look at B again--->>over crowding MAY be the cause..MAY NOT be the cause as welll - in case of gowtham..doesn't nail it.

E confirmed !!

garbus222 wrote:
Can somebody please be so kind as to explain me why the ans is E and not D (example comes from Kaplan's GMAT 800 - but I still don't get the explanation).

Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools.

Which of the following, if true, most seriously weakens the argument above?

A. The high school system in Gotham succeeds in giving students a good education at considerably less cost than do most systems.

B. Several cities have found that overcrowding in the schools is not always associated with lower reading scores.

C. Gotham schools have a greater teacher-to-student ratio than most other school systems.

D. Students' reading skills have not declined in other cities where the high schools are just as overcrowded as those of Gotham.

E. Schools are not overcrowded in many cities where high school reading scores have declined more than they have in Gotham.

Why E??? For me it's clearly D because:
1) it offers alternative explanation (there must be some other reason for decline in reading skills than overcrowded schools)
2) E talks about "scores" not "skills" - isn't it a shift of scope?
Re: Causation question   [#permalink] 07 Apr 2008, 12:31
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