LSAT 141 | Section 4 | Logical Reasoning: Q3

LR Question 3 Explanation

QUESTION TEXT: Moore: Sunscreen lotions, which are designed to block…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Sunscreens don’t help reduce UV radiation.

REASONING: People who frequently use sunscreen get as much skin cancer as those who don’t.

ANALYSIS: This argument sounds persuasive, but it’s bad science. To do a proper experiment, you need a control group. You would take 1,000 people, randomly instruct half of them to wear sunscreen, give the other half no instructions, then compare results.

The reason for random assignment is that otherwise there may be relevant differences between those who do and don’t wear sunscreen.

For instance, maybe those who spend more time in the sun also use more sunscreen. They get more UV radiation, and are more at risk of skin cancer. If their skin cancer rate isn’t higher, then sunscreen is likely reducing UV radiation.

___________

1. The argument wasn’t talking about the other effects of sunscreen. This isn’t relevant.
2. This is a relevant difference, but we have no reason to expect that the non-sunscreen group had more severe skin cancers.
   Absent any other information, we can assume that if two groups have the same number of cancers, then the severity of those cancers is comparable.
3. The stimulus said that all sunscreen is designed to block UV rays. So there are no other sunscreens to consider.
4. It’s very possible to challenge the evidence. You’d just have to check the source of the cancer statistics and see if everything checked out. Numbers are either right or wrong: they’re easy to challenge.
5. CORRECT. This is a relevant difference. If people who use sunscreen spend more time in the sun, they are exposed to more UV radiation. The fact that they don’t have more cancer is evidence that sunscreen does block UV rays.