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Complete Question Explanation

Flaw in the Reasoning—#%. The correct answer choice is (B)

Based on the premise that roads with bicycle lanes have more car-and-bike collisions than roads without such lanes, the author of this stimulus concludes that the addition of bicycle lanes to existing roads would not be likely to make cyclists safer:
  • Premise: ..... Roads with bike lanes have more car/bike accidents.

    Conclusion: ..... Adding such lanes to existing roads would not likely increase cyclists’ safety.
The author’s argument implies that bike lanes may cause safety levels to decrease (at the very least, they do not lead to increases in safety for bicyclists). One issue with this argument concerns the limited information provided. Knowing that roads with bike lanes suffer a greater number of bike and car collisions is not very helpful without knowing something about the percentages of bikes that collide with cars, and how those figures compare. One might expect, for example, that roads with bike lanes might draw more cyclists, which could be an alternative cause for the greater number of referenced collisions.

The question asks for the flaw in the author’s reasoning. As discussed, the author’s conclusion is based on limited information.

Answer choice (A): The author need not have addressed the possibility that the seriousness of injuries sustained in car-and-bicycle collisions might be about the same regardless of the presence of bike lanes, because the author’s conclusion does not rely on this comparison. While this choice might strengthen the author’s argument, its absence is not a flaw in the author’s reasoning, so this answer can be ruled out.

Answer choice (B): This is the correct answer choice. As discussed above, the author fails to consider that roads with bike lanes are likely to attract more cyclists. If that is the cause of the greater number of bike-and-car collisions, rather than the mere presence of bike lanes, then this would significantly weaken the author’s conclusion.
  • ..... ..... ..... ..... ..... ..... Cause ..... ..... ..... ..... Effect
    Author’s implication: ..... Lower level of safety ..... :arrow: ..... Greater number of car-bike collisions
    This choice: ..... ..... ..... More cyclists ..... ..... :arrow: ..... Greater number of car-bike collisions
If a road with a bicycle lane draws more cyclists, then comparing just the number of car-bike collisions is meaningless without information on how the percentages compare.

Answer choice (C): The author does not assert, or imply, that every safety enhancement will benefit both cyclists and motorists, and the author’s conclusion is only about the safety of cyclists, so this choice can be quickly ruled out of contention.

Answer choice (D): The author of the stimulus does not assert that only some bike-lane-equipped roads are safe, but rather that such roads (in general) have more bike-and-car collisions than roads without such lanes. Since this choice does not actually reference a premise used by the author, this cannot be the correct answer choice.

Answer choice (E): This choice was appealing for many test takers, because the argument’s flaw can be expressed as statistical in nature. The problem, however, is that the author does not conclude that anything is proven. Rather, the author takes limited statistical evidence (more accidents on roads with bike lanes) which seems to lack support for the increased-safety-proposition, and concludes that adding bike lanes is unlikely to increase safety levels. This is not the same as proving the opposite conclusion, and this choice fails to specify the real flaw in the author’s argument, so this cleverly worded choice should be ruled out of contention.
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Can you just explain to me where I'm going wrong with this analysis?:

To begin, I completely see and understand why B. is correct. What I would like to clarify is why A. is incorrect. Your original post explains that it doesn't relate to the argument-- but I think it does. Here is my reasoning:

The stimulus says that there are more collisions when there are bike lanes --> so, adding these lanes is unlikely to enhance the safety.

Answer choice A. states that it overlooks the difference in seriousness of accidents between on roads with and without lanes.

So, let's say that far more accidents occur when there are bike lanes, but 100% of these accidents resulted in minor scrapes and bruises. Now, let's say, that without bike lanes, less accidents occur, but of the accidents that DO occur, 100% of accidents were fatal.

Then, you would argue that actually, no, the bike lanes DO enhance the safety of the bicyclists.

Is my analysis incorrect here because I'm treating it as a weaken question? Perhaps answer A. weakens it but isn't the direct flaw? I'm not sure why A. isn't a flaw in their reasoning that the added lanes don't enhance safety. But, once again, I do see why B. is a better answer. Honestly, I had prephrased something along the lines of A. (I recognized a gap between the terms accidents and safety), saw A., selected it, and moved on. Had I read B., I would have selected B. This goes to show that I need to be a bit more careful, but I am a strong LSAT taker and typically have no problems with skipping over other answers when I find my prephrase.

Thanks for clarifying!
 Eric Ockert
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Hi Kristin!

The explanation said the conclusion doesn't rely on this comparison, not that it doesn't relate. You are right that it definitely does relate. The severity of the injuries could definitely be relevant to this argument for the reasons you laid out.

However, take a closer look at answer (A). It states that the author "overlooks the possibility...." This is a common construction on Flaw in the Reasoning answer choices. One way to think of these answers is, if the author is overlooking that possibility, that means the author is assuming that statement does not exist.

So here, if we negated the statement in answer (A) it would read: "injuries sustained by bicyclists in accidents on roads with bicycle lanes are NOT as serious, on average, as those sustained by bicyclists in accidents on roads without such lanes." So, the question then is, did the author assume this? Not at all. The author is really not making any assumptions about the severity of injuries in these accidents. That's what the explanation meant when it said the author did not "rely" on this information.

The author is really just assuming that more accidents means more danger. Danger, however, is really more about risk, which is really the probability or percentage chance of being harmed. An assessment of percentage would require knowing the total number of bicyclists. That's what answer choice (B) gets at.

Hope that helps!

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