Q9 - Chronic fatigue syndrome, a condition

[cvfh17]

I'm completely lost with the argument with B hte correct answer and what about the other answers? thanks

[ohthatpatrick]

See if you can tell me what's wrong with this argument:

Cristal, a premium alcoholic beverage that sells for $200 / bottle, is invariably bought by wealthier-than-average people. Further, Dom Perignon, a very pricey champagne is also associated with many affluent consumers. These facts in themselves demonstrate that buying very expensive alcoholic beverages would provide an effective path to financial prosperity.

Say what?

This author is thinking that since pricey alcoholic beverages go hand in hand with wealthy consumers, it must be that buying these beverages makes a person more wealthy.

This is obviously ridiculous, as we would be more likely to assume that being wealthy allows someone to buy expensive beverages.

However, this is the same reasoning pattern LSAT wants us to identify and attack:

A correlation between two factors, A and B, does not prove that either one has any causal influence on each other.

(It does strengthen the idea that one has an influence on the other, but it doesn't demonstrate , as this author says, or prove that one thing has an influence on the other)

A correlation between A and B could mean:
- a coincidence
- A causes B
- B causes A
- Both A and B are caused by some third factor, C

In Q9, the argument core is this:

Conc: raising magnesium in the blood would provide a cure for the fatigue of CFS.
why?
Prem: CFS is invariably associated with lower-than-normal magnesium in the blood.

The middle sentence is somewhat of a premise, as it adds yet another correlation between lower magnesium in the blood and fatigue. However, since the conclusion is about the fatigue involved in CFS, the first sentence is more directly applicable.

This argument is BRUTAL to evaluate in real-world, biological terms. What we non-scientific LSAT students are supposed to see is merely the fact pattern:
CFS is invariably associated with low Mg in the blood
Thus,
higher Mg in the blood would cure CFS

What this is implicitly assuming is that the low Mg causes the fatigue.

All the first two sentences give us are correlations between fatigue and low Mg.

What wording in each of those sentences tips us off to a "correlation"?

X is associated with Y

Other versions of that you might see are:
- ppl who are X are more likely to be Y
- having the quality of X tends to be accompanied by having the trait of Y
- while X was occurring, Y was occurring

As soon as we see a correlation, we want to be on guard for an author claiming or assuming that X causes Y.

When we see that in the conclusion, we want to skeptically think, "What if Y causes X? What if some third factor Z actually causes both of them? What if it's just a coincidence?

(B) addresses reverse causality. This is the most devastating objection to a correlation -> causality type argument. In order to believe that X causes Y, we NEED the author to rule out the possibility that Y causes X.

If it were true that fatigue causes low Mg, then this argument would sound stupid. It would be as crazy as my original example, thinking that buying expensive alcohol caused someone to be wealthy, rather than the other way around.

=== other answers ===

(A) It is true that the argument fails to do this. But, do we NEED the author to do this? I don't care if low Mg is ALWAYS due to malabsorption of Mg. In fact, the author is already implying that low Mg is sometimes due to malabsorption, sometimes due to Chronic Fatigue Syndrome.

I care if low MG is EVER the cause of fatigue.

(C) Would it hurt the author's argument to establish that some people's Mg level fluctuates? Doesn't seem to. He's talking about people who have lower-than-normal Mg in their blood, but that doesn't have to mean it's a CONSTANT, unchanging level. It could be that everybody's Mg fluctuates, but these lower-than-normal people's Mg fluctuates in a lower range.

(D) It's true he fails to do this. Does he NEED to state the exact concentration of Mg which is normal? Of course not. We're not doctors. We're not here to analyze the specifics. We're here to analyze the reasoning. Did I need to specify the exact income level meant by "wealthy" for you to judge that my original example was bad logic?

(E) This goes beyond the scope of the conclusion. IF we accepted his conclusion and believed that low Mg causes fatigue, THEN we would possibly care about how best to raise someone's Mg. But on LSAT, we DON'T accept the conclusion, so we need an answer choice that FIGHTS the idea that low Mg causes fatigue.

Let me know if you still have questions.

[ZZ927]

Patric,

I would love to spend some time to praise you on your dedication on LSAT and other test prep classes you teach (if there is any). I have been struggling with LSAT for few months, and I am no where near the finishing line. Over my course of study, I found your explanation extremely helpful. You don't use any unnecessary jargon (even if you do, you always have an explanation in parentheses). I found your posts super didactic, informative and easy to read! This means the world to anyone who is currently struggling with LSAT, especially students like myself, ESL learner who is really shooting the star. Thank you so very much for making my progress possible! You are my hero and my male version of statue of liberty! Thanks a million plus one time!