Logical reasoning PrepTest 131 · Section 1 · Question 4

Incorrect. The dermatologists are appealed to as authorities on skin treatment, not as a representative sample of all doctors or all people who might use the skin cream. As such, there's not a sampling flaw here.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Dermactin consulted dermatologists during its development, so 75% of surveyed dermatologists prefer it to all competitors, and thus you should use it if you need skin cream.

Answer Anticipation:
There are two key elements in this stimulus that suggest certain flaws.

First, the argument relies on the opinion of dermatologists to reach its conclusion. However, it's discussing a skin cream, which would fall under the dermatologists' area of expertise, so this is an appropriate appeal to authority and thus not a flaw.

Second, the argument relies on a survey of these dermatologists, highlighting that 75% prefer Dermactin to all other brands. Surveys, studies, and polls all suggest sampling flaws, and correlation/causation flaws. There's no correlation here, so there can't be a correlation causation flaw.

There's no specific reason to doubt the sample—it doesn't bring up a way that this group could be unrepresentative, and it doesn't mention the sample size ("3 out of 4 doctors surveyed . . . ". Normally, when there's a sampling flaw, there will be reason to question the sample provided in the stimulus. However, since there's no other flaw that we can identify, let's expect the answer to bring up a consideration that calls the sample into question.

Answer Explanation:
This answer establishes a potential sampling flaw in the stimulus—too few dermatologists were surveyed. If that 75% represents 3 of 4, then there might need to be a wider survey done before we're confident in the results. Note that there was no reason in the stimulus to question the sample size, but this answer choice raises it as a possibility, and so it's the correct answer.

Key Takeaway:
Usually when there's a sampling flaw, the stimulus gives you a reason to believe that the sample is too small, unrepresentative, or not randomly split between groups. However, that won't always be the case. Whenever there's a survey/study/poll done in a stimulus, there's always the chance that an answer will establish a detail that calls the sample into question, even if the stimulus doesn't, so be on the lookout for it.

Incorrect. It doesn't presume that some dermatologists are better than others—it uses the fact that the majority of surveyed dermatologists prefer Dermactin to all others to support its conclusion. That doesn't discount the opinion of the other 25%, it just shows that they're in the minority and thus expert consensus lies elsewhere.

Incorrect. The argument relies on an appeal to expert authority, not consumers. This answer would be more appropriate if the stimulus used sales to determine effectiveness.

Incorrect. The conclusion is qualified, limiting itself to those who need skin cream, so those who don't use it (and thus don't need it) are out of scope.