LSAT Weaken question

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nonameee: Master | Next Rank: 500 Posts; Posts: 111; Joined: Mon Oct 03, 2011 12:08 pm

by nonameee » Fri Dec 02, 2011 6:41 am

Chronic fatigue syndrome, a condition that afflicts thousands of people, is invariably associated with lower-than-normal concentrations of magnesium in the blood. Further, malabsorption of magnesium from the digestive tract to the blood is also often associated with some types of fatigue. These facts in themselves demonstrate that treatments that raise the concentration of magnesium in the blood would provide an effective cure for the fatigue involved in the syndrome.

The argument is most vulnerable to which one of the following criticisms?

(A) It fails to establish that lower-than-normal concentrations of magnesium in the blood are invariably due to malabsorption of magnesium.

(B) It offers no evidence that fatigue itself does not induct lowered concentrations of magnesium in the blood.

(C) It ignores the possibility that even in people who are not afflicted with chronic fatigue. Syndrome concentration of magnesium in the blood fluctuates.

(D) It neglects to state the exact concentration of magnesium in the blood which is considered the normal concentration.

(E) It does not specify what methods would be most effective in raising the concentration of magnesium in the blood.

B

Can someone please explain the logic behind the OA?

Thanks

Source: Beat The GMAT — Critical Reasoning | Fri Dec 02, 2011 6:41 am

nonameee: Master | Next Rank: 500 Posts; Posts: 111; Joined: Mon Oct 03, 2011 12:08 pm

by nonameee » Fri Dec 02, 2011 6:48 am

I got it right after I posted the question:

The author claims that since the level of magnesium in blood and stress are correlated, increasing the level of magnesium will alleviate the stress. However, the fact that two things a correlated doesn't necessarily imply that one thing causes the other. For all we know, stress might be the cause of low level of magnesium and increasing the level will not help to reduce the stress (since the level of magnesium in blood doesn't cause stress).

GmatVerbal: Master | Next Rank: 500 Posts; Posts: 138; Joined: Thu Nov 12, 2009 10:07 amFollowed by: 3 members; Thanked: 19 times

by GmatVerbal » Fri Dec 02, 2011 9:28 am

This is a causal argument
X( low levels of magnisium ) , Y(fatigue) are observed together; so X is the cause for Y;

flaw: guilty by association:

weakness: Y could be causing X; or Z(someother reason) could be causing it;

This is a pretty basic question covered in OG. Have you finished doing OG, if not I would suggest you to finish it first. Then go to LSAT questions. That way you can cover your bases. Just a friendly suggestion, no offense.

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