Logical Reasoning

PT146 · S3 · Q21 Journalist: People whose diets contain

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Journalist: People whose diets contain a relatively large amount of iron are significantly more likely to develop Parkinson’s disease than are those whose diets contain less of this mineral.

Conclusion (should thus)

Limiting one's intake of meats, seafood, and other foods rich in iron should reduce one's chance of contracting Parkinson's disease.

Evidence (people who are X more likely Y)

There's a correlation between

diets contain | | more likely to get large amount Parkinson's of iron

Evaluate

When an author presents a Curious Comparison like a correlation, they will almost always then make some causal assumption about one side causing the other.

In this case we can tell the author is assuming that

eating diet with leads to higher chance of lots of iron Parkinson's

because her conclusion is acting like

avoiding a diet would help lower chance of high in iron Parkinson's

Whenever an author assumes some causal explanation for a curious fact, we react with two different questions: - could there be some Alternate Explanation for the curious fact? - how plausible is the Author's Explanation

Goal

Since this is Strengthen, we want to either - rule out a different way to explain why a diet high in iron is correlated with higher Parkinson's risks (i.e. )

- increase the plausibility that high iron leads to higher Parkinson's risk, or that eating less meat / seafood / iron-rich food would help lower one's Parkinson's risk.

21.

Which one of the following, if true, most strengthens the journalist's reasoning?

Correct
Most people who have a
Why this is right
This rules out an alternate explanation. Whenever we're presented with a correlation between X and Y, and the author concludes that X causes Y, we'll come back at him with two classic Alternate Explanations: - what if Y causes X (reverse causality) - what if Z is the reason Y and X are correlated (third factor) In this argument, reverse causality would be nonsense, because "more likely to develop" Parkinson's implies that Parkinson's came later. We can't argue that Parkinson's came first and it led to a higher iron diet. But we can still argue that some third factor is causing the higher Parkinson's risk, and it's either causing or correlated with higher iron diet, which is why there appears to be a correlation between Parkinson's and high iron. Having a lot of money could simultaneously cause you to eat caviar and play golf. If we cited a correlation that "people who play golf are more likely than those who don't to eat caviar", we wouldn't want to assume that playing golf is what's causing you to eat caviar. Similarly, a certain genetic profile might lead to both higher risk of developing Parkinson's as well as some form of anemia (iron-deprivation). That sort of person would both have to eat a high iron diet and be at high risk of developing Parkinson's. Thus, there would be a correlation between high iron and higher rate of Parkinson's, even though neither one is causing the other. When a Strengthen answer is ruling out an alternate cause, it's "controlling" for some other variable, so we frequently hear the language were no more likely to or something equalizing like that. If people with a genetic bent towards Parkinson's are no more likely to have a high iron diet, then it rules out the possibility that high iron is just a coincidental factor that's "riding on the coattails" of the real causal factor ... genetic predisposition.
Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.
65% picked this
Many of the vegetables regularly
No Impact
When authors list examples, as this one did by citing 'meat, seafood, and other foods rich in iron", the named examples are not important at all. But LSAC likes to write trap answers trying to get people to care. The logical force of meat / seafood / veggies consumed by vegetarians is all the same: high iron. Being told that some veggies are also high in iron means nothing. It doesn't help us investigate whether these high iron diets (whether that iron is coming from meat / fish / veggies) is the causal factor creating a higher risk of Parkinson's.
5% picked this
Children and adolescents require a
Irrelevant Comparison
The fact that kids are more likely to eat iron than adults doesn't have any clear impact on whether high iron has a causal effect on Parkinson's risk. We're trying to compare people at the same stage of life in terms of more iron / less iron in their diet. The author is thinking, given two 30 year old people (or two 40 year old's, or two 10 year old's), the person limiting their intake of iron-rich foods will be less likely to develop Parkinson's.
4% picked this
The iron in some foods
Too Weak
This is such a weak idea. When you woke up today, did you think that "Every single food in the world was identical in terms of how quickly the body can absorb its iron content"? Of course not. So this answer is only telling you what you already knew from common sense. - differences and fluctuations exist
23% picked this
The amounts of iron-rich foods
Irrelevant Distinction
This is similar to (C) in the sense that we aren't interested in comparing one age group to another, since the argument never cared about that. We're only interested in comparing people of any given age group with an iron-rich diet to people of that same age group with a less iron-rich diet, in relation to whether or not they have or ultimately develop Parkinson's.
4% picked this

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