On the first day of trout season a team of biologists went

Question

On the first day of trout season a team of biologists went with local trout anglers to the Oslo River. Each angler who caught at least 2 trout chose exactly 2 of these trout for the biologists to weigh. A total of 90 fish were weighed. The measurements show that at the beginning of this season the average trout in the Oslo River weighed approximately 1.6 kg.

The reasoning above is most vulnerable to criticism on the grounds that it

A. Makes a generalization from a sample that is unlikely to be representative.
B. Relies on evidence that is anecdotal rather than scientific
C. Ignores the variations in weight that are likely to occur over the whole season
D. Fails to take into account measurements from the same time in previous seasons. 
E. Does not consider whether any fish other than trout were caught

IanStewart · Answer

The answer is A: there is little reason to think the trout that were weighed represent all the trout in the river. First, the fishers selected which trout would be weighed. They might have had some reason (if fishing policy was to be based on the weights, say) to select especially light or heavy trout. But it also could be true that larger trout are more likely to be caught by the fishers in the first place, in which case even weighing all the caught trout wouldn't produce a good estimate of the average trout swimming in the river.

TheNightKing · Answer

I don't exactly understand what's happening in this question. Can someone try to explain the argument first and then answer choices?

Thank you!

Alamir · Answer

Anytime you see numbers in the question and one of the answers says the sample is not representative. It is the right answer

idonquit · Answer

Find this explanation of Nathan Fox, a LSAT teacher. Hope this help.
Based on their terrible sampling, the only valid conclusion that could have been reached here is, “The average weight of the two trout chosen by fishermen who caught at least two trout today is X.” You cannot make any valid conclusion about the average trout in the river.
There are not one but two reasons to believe that the sample is unrepresentative here. First, the trout weren’t randomly selected from the river: they are the ones that were caught by fishermen. Maybe they were caught because they are different in some way! They could be bigger than average, and that’s why they were caught. Or they could be younger and less experienced than average, and that’s why they were caught. Or they could be slower, dumber, lazier, hungrier—they could be different from the average trout in a million ways. So the sample may not be representative of the population as a whole.
And that’s not even the worst of it. The fishermen were then allowed to choose two of their trout to present for weighing! What, do you think the fishermen are going to show you the two trout closest to the average size of all the ones they caught? If that’s what you think, then you’ve never met a fisherman. And even without any outside knowledge, you should at least recognize that it’s not good science to let someone select which subjects will be used in a sample—the sample should be random! Either weigh all the trout that were caught, or randomly select from the trout
that were caught, but for Chrissakes don’t let Grandpa Skidmark limp over with his two biggest ones to brag about.
Okay, that’s gotta about take care of it. The answer is going to be “biased sample” or “unrepresentative sample.” Guaranteed.
A) Yes, this is exactly what we were looking for.
B) Well, it was certainly bad science, but I don’t know about anecdotal. “Anecdotal” would have been going down to the campfire and asking a couple of drunken fishermen what size trout they caught that day. I don’t think 90 trout is “anecdotal.” As bad as the science might have been, I don’t think this answer choice does a good job of describing it.
C) No, the conclusion was only about the weight of the trout at the beginning of the season, using fish that were caught on the first day of the season. Later variation is irrelevant.
D) No, the conclusion was only about the weight of the trout at the beginning of this season. Prior seasons are irrelevant.
E) No, the conclusion was only about trout.

gmat102021 · Answer

Hi  idonquit

is mentioned, so why can't we say C?
Also, A & C are the same in different words

On the first day of trout season a team of biologists went

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On the first day of trout season a team of biologists went

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