LSAT 69, Logical Reasoning I, Q3

QUESTION TEXT: A study of the dietary habits of …

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Galactose causes cancer, if you have more of it than you can process.

REASONING: There are two groups, one with cancer and one without it. Each group ate a similar amount of Yogurt, which has galactose. The cancer group didn’t have enough enzyme to process galactose.

ANALYSIS: This question makes a causation-correlation error. The fact that two things happen together doesn’t mean one causes the other.

The group already had cancer. Maybe their cancer lowered their production of the enzyme. Then cancer would be the cause of galactose malabsorption, and not the reverse.

Or maybe a third factor causes both cancer and the reduction in the enzyme.

___________

1. This sounds tempting, but it’s not necessary. Read carefully. It asks whether:
   1. Everyone’s diet
   2. was exactly the same
   3. in all other respectsNo medical study meets this standard. It’s impossible. People’s diets are very different. A study can still tell us something, even if not every variable is controlled with perfect accuracy.
2. The argument is just making a claim about galactose. It doesn’t have to make practical recommendations to improve people’s lives.
3. The argument doesn’t have to describe every possible cause of cancer. There are thousands of causes. The argument didn’t say that galactose is the only cause of cancer.
4. CORRECT. If cancer causes low enzyme levels, then galactose malabsorption is an effect of cancer, not a cause.
5. The groups were presumably somewhat large. If one person in a group lacked the enzyme, that shouldn’t affect the overall study.

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