Flaw in the Reasoning—CE. The correct answer choice is (D)
This author presents the results of a study of two groups of people—one group of people who had recently developed cancer, and one group without cancer. During the five years leading up to the study, the two groups consumed similar amounts of yogurt, which contains galactose, a substance processed by an enzyme in the body.
The group with cancer did not have sufficient levels of the enzyme to process the galactose in the yogurt they ate, so the author concludes that excessive galactose causes cancer:
- Premise: Those with cancer were the ones who were unable to process all of the galactose they consumed.
Conclusion: Galactose in excess of the body’s processing ability causes cancer.
The author’s argument is somewhat questionable, in that he or she notes a correlation between the inability to process galactose and the presence of cancer, and concludes that the excess galactose must be the cause of the cancer.
The question that follows the stimulus asks for the answer choice that weakens the author’s argument. The correct answer choice will undermine the author’s causal conclusion (that the excess galactose is the cause, and cancer is the effect).
Answer choice (A): There is no way to maintain perfect controls on every factor—the study was centered around the body’s absorption of galactose, and the dietary habits of the people do not need to have been the same in all other respects. Since this is not the causal flaw reflected in the stimulus, this cannot be the right answer to this Flaw question.
Answer choice (B): The recommendation in this choice is based on the author’s questionable conclusion that excess galactose is carcinogenic. Even if that conclusion were not questionable, however, the argument would not require that such a recommendation be made. In any case, this is not the causal flaw prephrased above, so this is not the flaw in the author’s reasoning.
Answer choice (C): The fact that other carcinogenic substances exist is not relevant to the argument in the stimulus; focusing on only one such substance is a common approach—it is not a reasoning flaw, so this choice should be eliminated from contention.
Answer choice (D): This is the correct answer choice. The author jumps to the conclusion that excess galactose must cause cancer:
- Cause Effect
…without considering the possibility that cancer leads to low enzyme levels (and correspondingly excessive galactose levels):
- Cause Effect
Answer choice (E): The focus is on the fact that for the cancer patients, the enzyme level was insufficient to process the galactose they were consuming; there is no need to specify whether anyone lacked the enzyme entirely, so this choice does not describe the flaw in the author’s reasoning.