Logical reasoning PrepTest 148 · Section 3 · Question 18

Incorrect. The argument uses a correlation in an attempt to establish a genetic basis for one trait—it doesn't assume this is true for all traits.

Incorrect. Since the conclusion is just that there are some cases of genetically determined dislike of vegetables, the volunteers don't have to be representative—if only the people in the survey had their taste in vegetables determined by genes, the conclusion would still hold.

Incorrect. This answer can be rephrased as: Even when something always causes an effect, that effect could have other causes. Here, the argument doesn't establish or conclude that genes always determine taste in vegetables—in fact, the conclusion says "at least in some cases."

Incorrect. That would be fine for the conclusion, which just states that taste is genetically determined, even if that's by other genes.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
In a study, some people liked vegetables and others didn't. Those who didn't all had the XRV2G gene, so at least some cases of vegetable dislike is caused by genes.

Answer Anticipation:
The argument here uses a correlation between a gene and a dislike of vegetables to establish that there is a genetic cause for that dislike, which is a flawed jump. However, here, with the way the study was set up, we can get a bit more specific. The gene in question is stated to be present in all of the volunteers who disliked vegetables, but it's not established whether the other group had the gene. In order for a correlation to actually show causation, it must be established that the effect is less prevalent when the cause is gone. Without completing the comparison between the two groups—without knowing that the group that liked vegetables didn't have the gene—there's no basis for stating that the genes are causing that dislike of vegetables.

As a somewhat facetious example, all of the volunteers who didn't like vegetables were in a study where scientists took blood samples. Using the logic in the stimulus, that would establish that, at least in some cases, being in such a study causes a dislike of vegetables. The issue there, of course, is that those who liked vegetables were also in that study!

Answer Explanation:
This answer highlights the incomplete comparison between the two groups in the study, highlighting why the correlation might not lead to causation. If everyone in the study had the XRV2G, then it's probably not what explains their different taste in vegetables.

Key Takeaway:
A causal relationship established in a study is strengthened by a control group—one where the cause isn't present, and the effect isn't, as well (or, at least, is present at a lower rate). When a study doesn't establish this no cause-no effect relationship, the correct answer in an Errors in Reasoning question might.