Logical Reasoning

PT119 · S4 · Q17 Researcher: Hard water contains more

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Researcher: Hard water contains more calcium and magnesium than soft water contains.

Conclusion (Thus)

People who drink mostly soft water incur an increased risk of heart disease, stroke, and hypertension.

Evidence (for)

People being treated for those three conditions tend to have lower Mg in their blood, and soft water las less Mg than hard water does.

Evaluate

The conclusion is making a causal claim (Doing X incurs an increased risk of Y), but none of the evidence was causal. So the author must be making some sort of causal assumption as she assesses this evidence.

She provided a Correlation, which is an LSAT author's beloved launchpad for a causal conclusion. The most common form of correlation language sounds something like:

people who are X are more likely than those who aren't to be Y

The final claim is basically saying .

Does the author think that being treated for these conditions causes you to have lower Mg in your blood? Or does the author think that having lower Mg in your blood causes these conditions?

She evidently thinks the latter, because she's envisioning this causal chain:

Drink mostly ⇢ Lower Mg ⇢ higher risk of soft water in blood these 3 ailments

We can use our Explain Curious Fact mindset, since the author is assuming a causal interpretation of a curious fact.

Curious Fact .. how come the people treated for these conditions have lower Mg in their blood? Author's Assumed Explanation .. lower Mg in your blood increases your risk of these three conditions.

We know we're supposed to consider 1. could there be an Alternate Explanation for that curious fact? 2. how plausible is the Author's Explanation?

If an author presents a correlation between X and Y and assumes that X causes Y, the two alternate explanations we want to always consider are: - REVERSE CAUSE (maybe Y causes X) - 3RD FACTOR (maybe both X and Y are attached to some third factor Z, which is the real causal factor)

Goal

On Weaken, when we're dealing with an Explain Curious Fact type reasoning move, the most common form of answer is to provide an Alternate Explanation for the curious fact.

So we would primarily look for a different way to explain why "lower Mg" and "these three conditions" are correlated.

But we can also consider any answer that would help us argue that drinking mostly soft water doesn't lead to a higher risk of those three conditions.

17.

Which one of the following, if true, most undermines the researcher's argument?

  1. Magnesium deficiency is not uncommon,

    No Impact

    Whether Mg deficiency is common or rare doesn't seem to really have any impact. We are only concerned with Mg deficiency, in those who have it, increases your risk of heart disease / stroke / hypertension. This answer doesn't help us assess that question at all.

    8% picked this

  2. Magnesium is needed to prevent

    Strengthens, if anything

    Our easiest reaction should just be "who cares what Mg is needed for", get out of here, (B). If we thought harder, and pulled in outside knowledge that LSAT wouldn't require of us, this seems to add plausibility to the idea that lower Mg could lead to those three conditions. The less Mg you have, the less you can prevent sodium from increasing your blood pressure, so the higher blood pressure you'll have. And higher blood pressure could increase your risk of at least some of those three conditions.

    2% picked this

  3. As people age, their ability

    Strengthens

    This is a confusing answer, because a lot of us see it as that 3rd Factor Alternate Explanation. "The real reason that lower Mg and these three conditions are correlated is because both things are more common among older people. Old age is causing the low Mg in the blood, and old age is causing the higher rate of heart disease / stroke / hypertension." That would totally work as an Alternate Explanation. But this answer isn't saying that older people have lower Mg in their blood. It's actually saying they have higher Mg in their blood. When you metabolize something, you break it down and excrete waste products. The fact that older people can't break down the magnesium means that more of it would build up in their blood. So, since this answer is actually ruling out the possibility that "old age is causing the lower Mg and higher rate of these conditions", it mildly strengthens the argument by ruling out an alternate explanation.

    9% picked this

  4. The ingestion of magnesium supplements

    Weak Impact

    This is a worse version of (E). It almost lets us build an alternate explanation for why the people with these conditions have lower Mg. "If you have one of these conditions, then you know that taking Mg supplements (which would give you higher Mg) would inhibit the effectiveness of your meds. So if you have heart disease, you will then avoid taking Mg supplements." In a sense, "Having one of these conditions" is leading to "not having higher Mg (from supplements". That's close, but (E) is giving us "Having one of these conditions" is leading to "having lower Mg". This answer would only make us think that people with these conditions would not have high Mg. They could still have normal Mg. (E) allows us to explain why they have lower Mg.

    14% picked this

  5. Correct

    Compounds commonly used to treat

    Why this is right

    This provides the Reverse Cause Alternate Explanation. There was a correlation between low Mg and higher risk of these conditions. The author assumed that, "first came the low Mg, and that paved the way for then developing these conditions". This answer is allowing us to argue an alternate explanation: "first came these conditions. Then people started taking medicines to treat these conditions, and those medicines had the effect of lowering the Mg of the the people taking them." By analogy, suppose we heard the argument, "People with glaucoma tend to have higher than average THC in their blood. So be careful, potheads, if you keep hittin' that reefer, you'll increase your risk of glaucoma." This answer choice is making this objection: "Wait a sec. The glaucoma came first. And their doctor prescribed medicinal marijuana. That's why the glaucoma patients have higher THC in their blood."

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

    68% picked this

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