PrepTest 119

Incorrect. Only if we knew that the associated heart conditions weren't common and thus the correlation isn't a great one could this answer affect the argument. Since we don't know the relative rate of these diseases, this answer is incorrect.

Incorrect. If anything, tying magnesium levels to heart disease strengthens this argument.

Incorrect. This can be a tempting answer, but what does a failure to metabolize magnesium mean for magnesium levels? Does it mean people absorb it less and their levels are lower; or they process it less and thus it stays in their system more? Also, the stimulus doesn't tie age into these conditions. Two reasons to eliminate this answer!

Incorrect. This argument is a step removed from both the supposed cause and effect in the stimulus. It discusses ingesting magnesium supplements instead of blood magnesium levels. It discusses treatment for heart disease instead of the development of that disease. That's two elements that are removed from the stimulus, so we can rule this answer out. Compare this to answer (E) after we look at it!

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Hard water has more calcium and magnesium than soft water
People with heart conditions tend to have less magnesium than others
Therefore - Drinking soft water increases your risk of heart conditions

Answer Anticipation:
Weaken questions tend to feature Correlation/Causation flaws, so we should always be primed to look for this flaw in this question type. And we see a causal conclusion here, stating that a certain group "incur[s] an increased risk" of something. So it's arguing that drinking soft water causes an increased risk of certain heart conditions.

Is that based on a correlation? It is—it's actually based on two correlations. First, those who are treated for the given heart conditions have less magnesium in their blood. Second, hard water has more calcium and magnesium than soft water.

So there are actually two jumps here we need to anticipate answers for.

The first is about drinking soft water and having lower levels of magnesium in the blood. Maybe magnesium that's consumed in water, or with calcium, doesn't make it into the blood. Or maybe drinking less magnesium results in your body getting more of it from food.

The second is the Correlation/Causation flaw. Assuming that those who drink soft water do have lower levels of magnesium in their blood, there's still the issue that the lower levels are only correlated with heart disease, they're not a cause of it. We can weaken that causal relationship by:
(1) Identifying an alternative cause (something that would lower blood magnesium levels and increase heart disease risk)
(2) Finding counterexamples (cause without effect, or vice versa; however, this argument is about an increased risk, so this answer isn't very likely since counterexamples don't disprove anything about risk)
(3) Bring up reversed causality (maybe the heart disease causes people to absorb or retain less magnesium)
That's actually quite a bit to juggle between both assumptions/flaws, so let's be careful as we work through the answers.

Answer Explanation:
This answer establishes that the correlation between magnesium levels and heart conditions is actually due to a causal relationship that is the reverse of what the Researcher concludes. She believes that drinking soft water causes a person to have less blood magnesium, causing heart conditions. This answer establishes that someone who is being treated for a heart condition is taking medication that will lower their blood magnesium levels—the reverse of that causal relationship. Note that this answer isn't similarly removed from both cause and effect as answer choice (D) is. It speaks directly to blood magnesium levels, and it also discusses people with heart conditions, as someone who is being treated for a heart condition almost certainly has one.

Key Takeaway:
Always focus on answers that directly address the supposed cause and effect when dealing with a Correlation/Causation flaw. The more removed an answer is from them, the less likely it is to be correct. Also, even if an answer doesn't match your anticipation, consider it if it mentions the cause or effect!