Logical Reasoning

PT147 · S1 · Q21 People with higher-than-average

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People with higher-than-average blood levels of a normal dietary by-product called homocysteine are twice as likely to be diagnosed with Alzheimer's disease as are those with average or below-average homocysteine levels.

Conclusion (Thus)

Including large amounts of B vitamins and folic acid in one's diet will likely reduce one's risk of developing Alzheimer's.

Evidence

People with higher than average levels of homocysteine are twice as likely to be diagnosed with Alzheimer's.

B vitamins and folic acid convert homocysteine into substances known to have no relation to Alzheimers' disease.

Evaluate

Since the evidence is dealing with a correlation (ppl who have trait A are twice as likely to have trait B), while the conclusion includes a causal verb (including large amounts of folic and B vitamins will reduce your risk), we can use our Explain Curious Fact mindset.

Curious Fact ... how come people with high homocysteine are twice as likely to have Alzheimer's?

Author's Explanation ... the high homocysteine is causing the Alzheimer's.

How do we know that the author is thinking that the high homocysteine is causing the Alzheimers?

Because the author is saying that by eating more folic acid / B vitamins, you'll break down (i.e. lower) your homocysteine, which will reduce your risk of Alzheimer's.

Our job with Explain Curious Fact arguments is to ask these two questions: 1. What could be an Alternate Explanation for the curious fact? 2. How plausible is the author's explanation?

Typically, when there's a correlation between X and Y and then the author assumes that X causes Y, we need to consider alternate explanations like Reverse Causality (Y causes X) or 3rd Factor (Z causes both X and Y).

So here alternate explanations could be that having Alzheimer's actually causes your homocysteine to go up, or that some underlying factor (maybe a genetic marker) causes someone to have higher than average homocysteine as well as elevated risk of Alzheimer's.

Goal

Let's look for an answer that suggests an Alternate Explanation (e.g., the high homocysteine was caused by Alzheimer's), or an answer that otherwise hurts the plausibility that having more folic acid and B vitamins in our system would lead to lower homocysteine which would lead to lower risk of Alzheimer's.

21.

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

Many Alzheimer's patients have normal
No Impact
This is a very weak claim saying that "at least 5 people with Alzheimer's have normal homocysteine". Okay ... was the author assuming that all Alzheimer's patients had abnormal homocysteine levels? No, so this has no impact. Whenever arguments are based on correlations (such as "people who are X are twice as likely to be Y"), we can't weaken that by pointing out that some exceptions exist (by saying "Some X's aren't Y").
13% picked this
The substances into which homocysteine
Out of Scope: not-Alzheimer's
This argument is only about whether adding certain things to our diet could reduce the incidence of Alzheimer's disease, so whatever other effects homocysteine might have that are unrelated to Alzheimer's wouldn't be relevant to this conversation.
4% picked this
B vitamins and folic acid
No Impact
This would only weaken if the author had suggested that we all start ingesting large amounts of folic acid and B vitamins -- this is saying that ingesting them via supplements probably wouldn't work very well.. This really has nothing to do with the argument; the author never said that ingesting large amounts via supplements would lead to a reduction in Alzheimer's.
8% picked this
People whose relatives contracted Alzheimer's
Weak Impact
This answer suggests that whether people get Alzheimer's has a lot to do with genetics (since it seems to "run in the family"). The author is thinking that our risk of Alzheimer's has a big environmental influence (since she is thinking that by altering our diet we could reduce our risk). So the more we think that Alzheimer's is genetically, not environmentally, determined, the worse this argument looks. But this answer still has limited impact. It isn't allowing us to assume that Alzheimer's is completely genetically determined. A lot of diseases have genetic and environmental components to it. A person from a family with a history of lung disease is at a higher risk of lung cancer, but they can still increase their risk even more by smoking cigarettes. So this answer suggests there may be a genetic component to developing Alzheimer's, but it doesn't do anything to reduce the idea that there could also be an environmental, dietary component as well.
6% picked this
Correct
Alzheimer's disease tends to increase
Why this is right
This suggests an alternate explanation for the correlation in the first sentence. It's not that higher homocysteine is causing the Alzheimer's; having Alzheimer's is causing the higher homocysteine. Whenever we see a correlation between X and Y that the author interprets to mean "X causes Y", we want to consider the alternate explanations of Reverse Causality (Y causes X) and 3rd Factor (Z causes X and Y). This answer is just doing the classic Reverse Causality alternate explanation. Once we realize that high homocysteine is an effect of Alzheimer's, not a cause of it, it weakens the conclusion that eating stuff in order to lower your homocysteine would lower your risk of Alzheimer's.
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
68% picked this

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