PrepTest 146

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
A diet heavy in iron is correlated with a heightened risk of Parkinson's, so people who want to limit their risk of Parkinson's should avoid iron-rich foods.

Answer Anticipation:
Strengthen questions frequently have correlation/causation flaws. Phrases such as, "significantly more likely," highlight correlations, and since we get that phrase early on in a Strengthen question, we can be pretty sure we know what direction this question is heading.

We get to the conclusion to see that it has assumed causality—to recommend that those who want to lower their risk of Parkinson's should avoid iron-rich foods, one must believe that an iron-rich diet causes an increased risk of the disease. Since this argument commits a correlation/causation flaw, we can strengthen it with the common methods:

(1) Eliminate an alternative cause
(2) Find more examples of the cause and effect going together
(3) Identify a control (no cause, no effect—but that's unlikely here since the stimulus already noted a higher incidence of Parkinson's, suggesting that those without a high-iron diet tend to not have the disease)
(4) An explanation of how iron causes Parkinson's

Answer Explanation:
While it takes a bit of thinking, this answer eliminates an alternative cause. It's possible that a genetic predisposition to Parkinson's in some way influences the diet to be heavy in iron, thus explaining the correlation without needing the causal relationship between iron and Parkinson's.

Key Takeaway:
Phrases that something is "more likely" found in a group are correlations, and you should start thinking correlation/causation flaw when you see that or a similar phrase. But be careful! Saying that something "makes" another more likely or "increases/decreases" the likelihood is a causal statement.

Incorrect. This answer highlights counterexamples—people who have a high-iron diet but don't develop Parkinson's—so it's more on the weaken side.

Incorrect. This issue is at best irrelevant to the argument, and at worst more on the weaken side assuming that children/adolescents have relatively iron-rich diets but have not (yet) developed Parkinson's.

Incorrect. The metric in the stimulus is the diet itself, not the levels of iron in the blood or absorbed into the body, and so this answer is out of scope.

Incorrect. First, there's no premise establishing when Parkinson's tends to develop. Second, assuming we bring in the outside knowledge that Parkinson's develops later in life (60 is the average age of diagnosis—thanks, internet!), this answer would undermine iron as a cause since diets are relatively light on iron by that point.