Logical Reasoning

PT139 · S1 · Q3 A study of the dietary habits

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A study of the dietary habits of a group of people who had recently developed cancer and a group without cancer found that during the previous five years the diets of the two groups' members closely matched each other in the amount of yogurt they contained.

Conclusion

If you have more galactose in your body than what the body can process, it is carcinogenic (cancer-causing).

Evidence

In a study, the group of people with cancer had such a low level of a certain enzyme that they couldn't process the galactose in the yogurt they were consuming.

Evaluate

The author is taking one fact she knows that is distinct to the cancer group and then concluding that that factor caused the cancer!

What if we had said, ? That would be a silly conclusion to reach. Maybe the hair loss is unconnected to the cancer. Maybe it's actually an effect of the cancer (or the chemotherapy treatment received by people who have cancer).

When an author presents a correlation, f.e. "the people who were X were also Y", she is likely to conclude that X causes Y. But we always evaluate causal arguments with the same two-pronged mindset:

- Is there any other way to explain this correlation? (maybe Y causes X. Maybe some third factor, Z, is causing both of them) - How plausible is the author's causal storyline? (is there any explanation of how X would cause Y? are there any data points that show when someone stopped having X, they stopped having Y?)

We are trained to react to correlations primarily by thinking,

Goal

Find an answer simply describing the author's illegal move of thinking, , or find an answer bringing up one of the alternative explanations the author has failed to consider:

3.

Of the following, which one constitutes the strongest objection to the reasoning in the argument?

  1. The argument fails to consider

    Weak Impact

    The author does fail to consider other possible differences in diet. We know they ate the same amount of yogurt, but we don't know how the rest of their diets compare. Learning about the rest of their diets, however, would only matter if we found something different in their diets that helped us find some other way to explain why the cancer / low enzyme group had cancer or low enzyme. It's not a strong objection to say to the author, "Hey, author, the dietary habits of every single person in two groups were not identical." You could have 99% of these people on identical diets, and one person eats 1.5 bananas / day while everyone else is eating 1 banana / day, and that sort of fact would already make it true that "the dietary habits of everyone was not the same in all other respects." That language is so extreme, that it's not a realistic demand we would make of any study that looked at people over a 5 year period.

    10% picked this

  2. The argument neglects to recommend

    Out of Scope: recommend

    The author is only trying to prove that X causes Y. Successfully proving that X causes Y doesn't require that you also advise people against doing X. Someone can prove that "smoking causes lung cancer" without ever saying "I recommend that people don't smoke", so the lack of a recommendation would never be a flaw in an argument that seeks to prove a causal relationship.

    1% picked this

  3. The argument focuses on only

    Out of Scope: other cancer-causes

    The author is only trying to prove that X causes Y. Successfully proving that X causes Y doesn't require that you also mention everything else that causes Y. Someone can prove that "smoking causes lung cancer" without ever saying "working in a coal mine also causes lung cancer". When we're making objections, we're saying "you failed to prove your conclusion", not "there are other things you should have also talked about beyond what your conclusion was saying".

    6% picked this

  4. Correct

    The argument overlooks the possibility

    Why this is right

    This is your classic Reverse Causality answer. The author presents a correlation: being in the cancer group was correlated with having low levels of the enzyme. Then the author assumes that low enzyme caused the cancer. What if cancer caused the low enzyme? Having a cancer or other illness can certainly affect your physiology in ways that may throw levels of certain body chemicals out of whack. Maybe the cancer came first and the low enzymes came second. The most common way to weaken a causal argument is to point out some other way to explain the evidence.

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

    81% picked this

  5. The argument does not specify

    Irrelevant

    We don't care whether anyone had zero enzyme. As long as the enzyme is "low enough" that the person can't process galactose, then the author can make the same argument. It doesn't matter whether that "low enough" is a tiny bit of enzyme, a speck, or nothing at all.

    1% picked this

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