Logical Reasoning

PT18 · S4 · Q9 Brain scans of people exposed

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Brain scans of people exposed to certain neurotoxins reveal brain damage identical to that found in people suffering from Parkinson’s disease.

Conclusion (Thus)

Brain scans can be used to determine who is likely to develop Parkinson's.

Evidence

Brain scans of people exposed to certain neurotoxins have damage that's identical to that found in people suffering from Parkinson's.

Intermediate Conclusion (This shows that)

These neurotoxins cause that type of brain damage, and that brain damage causes Parkinson's.

Evaluate

So this argument is saying that we can scan your brain and check for whether you have this telltale brain damage that the author thinks leads to Parkinson's, and thus brain scans can help us see who is likely to develop Parkinson's.

The author's intermediate conclusion introduces the idea of causality: neurotoxins cause the brain damage and the brain damage causes Parkinson's.

But the evidence doesn't have any causality. The brain scan just shows neurotoxins and brain damage. How do we know that the neurotoxins caused the brain damage? Could there be alternate explanations for why we see both? Maybe brain damage led to neurotoxins. Maybe some 3rd factor accounts for both the neurotoxins and the brain damage (taking too much nitrous oxide, for example).

Similarly, how do we know that this brain damage causes Parkinson's? Just because people with Parkinson's have the same type of brain damage as these neurotoxin people do? Maybe more than one condition could cause the same brain damage. Perhaps Disease X and Parkinson's both result in identical brain damage.

Goal

Since this is Flaw, we mainly want to react to this by thinking that one of the 10 Famous Flaws is Causal Overconfidence, in which the author is too confident to assume one possible causal explanation for the observed data.

The test wants us to either describe that overconfident causal inference or to point out the possibility of alternate explanations.

The argument contains which one of the following reasoning errors?

It fails to establish that
Not Necessary
Whenever a Flaw answer starts takes for granted / presumes / fails to establish, we can ask ourselves whether the idea that follows is a Necessary Assumption. Did this argument need to assume that "Other methods used to diagnose Parkinson's are less accurate than brain scans"? Nope. She's never arguing that brain scans are the best way to diagnose Parkinson's. She's only arguing that brain scans are a way to diagnose it its likelihood of developing.
2% picked this
It overestimates the importance of
Out of Scope: importance
The author is only claiming that brain scans can provide an early diagnosis. She's never saying that this is important or that people should try to get an early diagnosis. So we can't say she overestimated the importance of early diagnosis because she never comments on the importance of doing so at all.
1% picked this
Correct
It mistakes a correlation between
Why this is right
When a flaw answer says the author confuses X with Y mistakes X for Y we just want to check whether X sounds like the evidence and Y sounds like something the author concluded. Was there a correlation between the type of brain damaged described and Parkinson's disease? Yes, the author tells us that the type of brain damage we saw in these brain scans is the same as what we find in people suffering from Parkinson's. Did the author proceed to assume a causal relationship between the two? Yes, she said "This shows that the brain damage itself causes Parkinson's disease". That is definitely an illegal move. We're not allowed to think that just because two things are correlated that one of them definitely causes the other. That's one of the 10 famous flaws.
Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.
93% picked this
It assumes that people would
Not Necessary
Whenever a Flaw answer starts takes for granted / assumes / fails to establish, we can ask ourselves whether the idea that follows is a Necessary Assumption. Did this argument need to assume that "People want to know as early as possible whether they're likely to develop Parkinson's?" No, she isn't saying that people will want to use brain scans to determine whether they're likely to develop Parkinson's. Her conclusion is only claiming that brain scans could be used for that purpose. And there's nothing in the paragraph that has anything do with the extreme language of "as early as possible".
1% picked this
It neglects to specify how
Not Necessary
Whenever a Flaw answer starts takes for granted / presumes / fails to establish / neglects to specify, we can ask ourselves whether the idea that follows is a Necessary Assumption. Did this argument need to assume that "the brain scan information could be used to treat or monitor the progression of Parkinson's?" Nope. She's only claiming that the brain scans can allow us to see who is likely to one day develop Parkinson's disease.
3% picked this

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