Q3 - On the first day

[kmewmewblue]

So the reason why (A) is correct is that "A total of 90 fish to weigh" could be randomly picked?

Also, could you explain why (C) and (D) are wrong?
Thank you

[ManhattanPrepLSAT1]

Sounds like you see the issue on this one! The trout should have been selected randomly, rather than letting the fisherman choose the trout to be weighed.

The conclusion is that at the beginning of the season the average trout in the Macawber river weighed 1.6 kilograms. The evidence for this is that such was the average weight of the 2 trout selected by fisherman who caught at least that many trout. The issue is that the fisherman are likely to select the trout that were the largest and so the average weight of the selected fish should be an overestimate of the average trout in the Macawber river at the beginning of the season - best expressed in answer choice (A).

Let's look at the incorrect answers:

(B) is untrue. The evidence is not anecdotal since it does not just relay information conveyed by someone else.
(C) is untrue. The conclusion is not about the average weight of the trout in the Macawber river, but rather about the average weight of these fish at the beginning of the season.
(D) is incorrect for the same reason as answer choice (C) is incorrect. The conclusion is more narrowly focussed on the average weight of the trout at the beginning of the season, so it would be unnecessary to consider the weight of such trout during other seasons.
(E) is out of scope. Both the conclusion and evidence consider only trout, so other fish would be irrelevant.

Hope that helps!

[wj097]

The conclusion is that at the beginning of the season the average trout in the Macawber river weighed 1.6 kilograms. The evidence for this is that such was the average weight of the 2 trout selected by fisherman who caught at least that many trout. The issue is that the fisherman are likely to select the trout that were the largest and so the average weight of the selected fish should be an overestimate of the average trout in the Macawber river at the beginning of the season - best expressed in answer choice (A).

Hey mattsherman,

I had some follow up questions on your explanation for (A).
- How do you presume that "the fisherman are likely to select the trout that were the largest" and thus unrepresentative??
- In what circumstance would the sample be legitimate and not unrepresentative?? (i.g., large number trouts caught randomly, few trouts caught randomly, etc..)

Thx in advance

[jminton1]

The conclusion is that at the beginning of the season the average trout in the Macawber river weighed 1.6 kilograms. The evidence for this is that such was the average weight of the 2 trout selected by fisherman who caught at least that many trout. The issue is that the fisherman are likely to select the trout that were the largest and so the average weight of the selected fish should be an overestimate of the average trout in the Macawber river at the beginning of the season - best expressed in answer choice (A).

Hey mattsherman,

I had some follow up questions on your explanation for (A).
- How do you presume that "the fisherman are likely to select the trout that were the largest" and thus unrepresentative??
- In what circumstance would the sample be legitimate and not unrepresentative?? (i.g., large number trouts caught randomly, few trouts caught randomly, etc..)

Thx in advance

1. We presume this because anglers who caught more than 2 trout had their choice of which to weigh. This doesn't mean we can assume they chose the largest fish. Maybe they chose the smallest fish, or the most colorful fish. BUT since they made a choice the sample has to be unrepresentative.

2. I think any number of trout caught "randomly" can be representative. BUT it depends on the method used. So if the fisherman use a method that traps larger fish at a greater likelihood than smaller fish the sample will not be representative.

[Akyla T135]

If anyone is still struggling on this question I would like to provide my explanation as to why (A) is the correct answer.

Question Type: Classic Flaw

Stimulus Breakdown:
P: each angler who caught at least 2 trout chose exactly 2 of the trout to be weighed
P: 90 fish were weighed
C: measurement shows that average trout weighed approx. 1.6 kilos

Flaw: so at first glance I know automatically that we are dealing with the overgeneralization flaw because the measurement of 1.6 kilos is based on the average weight of trout selected by the anglers. The stimulus tells us that the anglers who caught at least 2 trout chose 2 of these trout to be weighed. We don't know how the anglers made their selection of the trout that were weighed. So my answer has to deal with the sample size being overgeneralized because the sample is not representative of the trout population as a whole.

Answer (A) does this