Q6 - Local resident: An overabundance of algae

[ohthatpatrick]

Question Type:
Flaw (vulnerable to criticism)

Stimulus Breakdown:
Conclusion: Too much algae must be harming the small fish in this pond.
Evidence: Over the last 15 years, whenever I've seen lots of small fish wash up dead, I've also noticed lots of algae.

Answer Anticipation:
It's the ol' Correlation vs. Causality flaw. The author presents a correlation: "whenever I see lots of dead small fish, I see lots of algae" and concludes a causal connection "the algae is causing the dead small fish".
We always have the same 2 prongs of attack:
1. Consider OTHER WAYS to explain the same evidence.
2. Consider the plausibility of the AUTHOR'S WAY.
In terms of #1, the most common alternative explanations are "maybe you have causality backwards --- maybe small fish dying cause there to be lots of algae" or "maybe there's some third factor that's really the reason for both --- maybe when the local oil company has a spill, it kills small fish and creates algae".
In terms of #2, maybe small fish actually LIKE having water high in algae. What if something about their diet or physiology actually thrives in the presence of high algae? In that case, something else must be causing the fish to die.

Correct Answer:
D

Answer Choice Analysis:
(A) Was this assumed? No, although normal people over-infer this sort of thing all the time -- "since you only talked about small fish, you must be saying the same thing DOESN'T apply to big fish". That's not a legal inference to make. I can truthfully say that "women who smoke cigarettes have an elevated risk of lung cancer". That doesn't commit me to the idea that "MEN who smoke do NOT have an elevated risk".

(B) Would this weaken? No. This protects the author's idea that algae is harmful to small fish. It just says that the harm wouldn't be as great in certain situations.

(C) Would this weaken? No. We don't care about fish of other sizes. We just care about what's killing all these small fish. Is it algae or something else?

(D) Would this weaken? Yup. It's the classic "third factor" objection to a correlation vs. causality argument.

(E) Would this weaken? No. Even if low algae is bad, high algae could also be bad. (Having too little iron in our diet is a problem, as is having too much iron in our diet)

Takeaway/Pattern: The most important reasoning archetype to master in LR is this correlation to causality one. Not only do we need to be great at recognizing these types of arguments, we also need to be good at setting up our 2-pronged prephrase "deals with OTHER WAY to explain, or deals with the plausibility of the AUTHOR'S WAY".

#officialexplanation

[tara_amber1]

Just wanted to throw my thought process out there on this question to see if it helps anyone else or needs some adjusting! Comments are much appreciated

Correct answer: (D)
Question type: Flaw

The core of the argument is that it moves from a correlation to causation. But we get the cause and effect relationship in the first sentence, then the resident shows supporting information for why he believes this to be true.

Just because there is an overabundance of algae and dead small fish doesn't mean that the former caused the latter. Perhaps there is a common cause or multiple causes for both of these events? A dirty pond that isn't well taken care of, something else in the water that causes contamination, etc. With this in mind we go to the answer choices.

(A) This seems like it would be the right answer, but we don't know anything about the large fish because they aren't mentioned in the stimulus. It does say smaller fish, but this still doesn't fix the weird situation going on.

(B) We're talking about a specific instance in "this pond." Who cares about larger bodies of water?

(C) Again, we don't know anything about fish of various other sizes and this doesn't detect the flaw we're anticipating.

(E) This answer I actually left open because it just looks like a trick. This kind of just restates the claim made in the first sentence.

(D), The correct answer, was easy to find if you were able to anticipate the flaw here. Dead small fish and the overabundance of algae could've had a common cause. Bingo!