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PrepTest 73, Logical Reasoning 2, Question 3


Question three, when a question asks for the criticism that an argument is most vulnerable to, you're dealing with a flaw question, which means you've been given a bad argument. And you have to find the error in that argument. But of course, before you can find the flaw, you have to understand the argument, which means understanding its conclusion and its evidence.

The conclusion of this argument comes right at the beginning. Sunscreen lotions, which are designed to block UV radiation, don't do so effectively. The evidence for the argument is a study that follows, well, not just a study, many studies, that have shown that people who consistently use sunscreen develop on average the same amount of skin cancer as people who don't use the sunscreens.

The flaw in this argument is another common one on the LSAT, a sampling error. Granted, there have been a lot of studies, but all those studies prove is that the rate of cancer amongst the various groups is roughly the same. They don't really explain to us why they're roughly the same. The only way that these studies can prove that sunscreen is useless is if we knew that there was nothing else other than sunscreen that could affect the rate of skin cancer that these people get.

If there's any difference between the groups, maybe the difference accounts for the similarity in skin cancer rates and not whether they use sun screen or not. And the most likely difference here is that people who choose to wear sun screen regularly might be doing so because they are vulnerable to skin cancer in some way. Think of it like insulin and diabetes. If your diabetes is controllable with insulin, your rate of fainting from a blood sugar crash would be roughly the same as a person who doesn't have diabetes and doesn't take insulin.

That doesn't mean that the insulin has nothing to do with stopping your fainting spells. It's the exact opposite. People who don't need to worry about fainting spells don't tend to take insulin. Taking insulin brings the rate of fainting back up to normal.

So there might be some reason that sunscreen users use sunscreen to bring them back up to normal. That's the flaw we're gonna be looking for when we go to the answer choices. So answer choice A says that the argument takes for granted that there are no other possible health benefits of using sunscreen lotions, and the other benefits is enough to kill this answer choice.

This argument is just about whether the sunscreen protect you from UV radiation. Whether it has some other benefits is entirely to the side of the point. So A isn't the answer. And to choice B, well this one is close to right. It'd be right to say that the argument ignores the possibility that even though the number of cancers is the same, the cancers of the non-sunscreen group might be more severe.

But this answer choice is saying that the argument fails to distinguish between number and severity. The argument doesn't confuse severity and number, it never brings up the difference between severity and number. So answer choice B isn't our answer. Answer choice C fails to consider the effectiveness of sunscreen lotions that are not specifically designed to block skin cancer.

And the problem with this answer choice is that the argument is only about lotions that are designed to block UV radiation. Ones that aren't, they're outside the scope of this argument too. So then answer choice D relies on evidence regarding the probability of people in different groups developing cancer that, in principle, would be impossible to challenge.

We have no information about the studies in this argument. So we don't know that the evidence would be impossible to challenge. We just know that this is what the studies have said. Whether it's challengeable is beyond the scope of the information we've been given. So that means that the right answer must be E. So let's see why.

E says, overlooks the possibility that people who consistently use sunscreen lotions spend more time in the sun, on average, than people who do not. Well, we said the flaw was forgetting that there might be something else affecting the skin cancer rates. Answer choice E is that the people who consistently use sunscreen lotion, maybe the reason they use it is because they are more vulnerable to skin cancer.

Thus, the lotion is bringing them back up to the normal rate of the people who don't have to use it because they're never going in the sun. Now, answer choice E is what we're looking for, and it is the answer.

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