Logical Reasoning

PT153 · S3 · Q17 After monitoring blood levels of lycopene

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After monitoring blood levels of lycopene (a nutrient found in some fruits and vegetables) in 1,000 middle-aged study participants over a 12-year period, researchers found that participants with low levels of lycopene were more than twice as likely as those with high levels to have a stroke during that period.

Conclusion (clearly)

Lycopene reduces the risk of stroke.

Evidence

In a study of 1,000 middle-aged people over a 12-year period, the people with low levels of lycopene were more than twice as likely as those with high levels to have a stroke during that period.

Evaluate

We've got the classic pattern of "Evidence = Correlation" and "Conclusion = Causality". The most common formulation for "X and Y are correlated" is to say . And then the conclusion is using the causal verb reduces.

Whenever the author's conclusion assumes to states a causal explanation for the curious comparison presented in the evidence, then we go into our Explain Curious Fact mindset.

Curious Fact ... why is low lycopene correlated with more strokes / why is high lycopene correlated with fewer strokes?

Author's Explanation ... Lycopene reduces the risk of stroke.

We always evaluate this template with the same two questions: 1. Can we think of an Alternate Explanation for the Curious Fact? 2. How plausible is the Author's Explanation?

Any time we're given a correlation between x and y, and then the author assumes or concludes that x causes y, we automatically react with these two alternate explanation possibilities: - could it be y causes x? (Reverse Causality) - could it be z causes x and y? (3rd factor)

Could having a stroke cause low levels of lycopene? Sounds weird, but maybe it's possible.

Could there be some 3rd factor that both explains why someone would have low lycopene and explain why they have more strokes than average? Sure, maybe there's a genetic condition that leads to both. Maybe the people who consume the least lycopene have some other behavior that increases their risk of stroke (perhaps bodybuilders avoid fruits and veggies in favor of protein, so they have low lycopene, and the strain that weightlifting puts on their bodies increases their risk of strokes. That would create a correlation between low lycopene and more strokes, even though the lycopene wasn't causing the strokes.)

Goal

Since this is Weaken, we primarily expect an answer to - suggest an Alternate Explanation for why low lycopene is correlated with strokes

but we'd also consider an answer that - hurts the plausibility of the Author's notion that lycopene reduces the risk of stroke

That parenthetical detail that lycopene is "a nutrient found in some fruits and veggies" feels like a Breadcrumb, like a detail that didn't need to be in the paragraph, so it's probably in there because the correct answer is going to use it in some way.

17.

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

Correct
Most fruits and vegetables that
Why this is right
Here we get a 3rd Factor Alternate Explanation. The real causal factors are nutrients XYZ. They reduce the risk of stroke. They happen to be found in fruits and veggies that are rich in lycopene. So people who eat these fruits and veggies are getting their risk of stroke reduced by nutrients XYZ. And they're simultaneously ingesting a lot of lycopene. This explains why there ends up being a correlation between lycopene and fewer strokes, but lycopene isn't the causal factor reducing the risk of stroke; nutrients XYZ are.
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
80% picked this
Countries in which people consume
Strengthens
This provides more data points that fit the author's hypothesis (More Cause, More Effect). She thinks that consuming lycopene causes lower risk of stroke, and this is talking about countries that eat a lot of lycopene and have a lower risk of stroke.
2% picked this
Middle-aged people typically have lower
Unclear Impact
Because the answer fails to tell us whether middle-aged people have more / fewer strokes than young adults, we can't really do anything with it. If we made a common sense guess that "the older you are, the higher your risk of stroke", then this would strengthen, because the older middle-aged people have lower lycopene and more strokes, just like the correlation in the argument. Just like (B), this would represent more data points that support the plausibility of the author's conclusion.
5% picked this
Study participants with high levels
No Impact
This is just explaining how they got higher lycopene, and it's probably what we were already assuming. If I tell you that lycopene is found in fruits and veggies and that Group A has more lycopene in their system than Group B does, then you'll probably think, "I guess Group A ate more fruits and veggies." This answer doesn't have anything to do with assessing the connection between lycopene and stroke or with a potential alternate explanation for why lycopene and stroke risk would be correlated.
8% picked this
There was wide variation in
No Impact
This is the classic wishy-washy wrong answer we see on Strengthen and Weaken: - things change - levels fluctuate - differences exist It tells us nothing we weren't already assuming. The results of the study are averaging together everyone's different lycopene levels and stroke risks and finding a strong correlation between the two. It doesn't matter that there was a wide variety of data points that went into that average.
5% picked this

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