Logical reasoning PrepTest 129 · Section 1 · Question 3

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Anglers that caught at least 2 fish picked 2 fish for the biologists to weigh. Based on this, the average trout was not 1.6kg.

Answer Anticipation:
While it never uses the word "study," this argument is very much set up as one, with scientists going out into the wild to measure something.

Whenever there's a study, you should start by considering a sampling flaw, and a correlation/causation flaw. We can quickly dismiss the second, however, as there's no causality in the conclusion (and no causal assumption, either).

So we should move on to considering a sampling flaw. Are the fish that the scientists weighed from a large, representative sample? 90 fish might be too small a sample, but it's not so small that we should anticipate the answer deals with that. But we can certainly tell that there's reason to believe the weighed fish aren't representative!

Here, the fish were selected by the anglers from among those caught. There's no indication that the caught fish were representative as far as weight is concerned (maybe smaller fish are more likely to be caught), and there's no indication that the fish selected by the anglers from their stock would be representative (maybe they picked the biggest ones to impress the biologists, or the smallest ones because the biologists released the fish they weighed back into the River). Let's find an answer pointing out that there's reason to believe the selected fish aren't representative of all fish.

Answer Explanation:
This answer highlights the unrepresentative sample, so it's the correct answer.

Key Takeaway:
A conclusion about "averages" suggests a potential sampling flaw; same with an argument relying on studies. Since we had both here, we could be pretty certain in our Anticipation of a Sampling Flaw answer!

Incorrect. The biologists went into the field with the anglers, so they're not relying on the anglers telling stories of the fish they caught.

Incorrect. The conclusion is about the average weight "at the beginning of this season," so variations over the course of the season are out of scope.

Incorrect. The argument doesn't compare the average weight this year to previous years, and it limits itself to discussing "this season," so other seasons are out of scope.

Incorrect. Other fish are out of scope of the argument, since the conclusion is about trout.