Logical reasoning PrepTest 141 · Section 4 · Question 3

Incorrect. Moore's argument and conclusion are just about the effectiveness in blocking skin-cancer-causing UV radiation, so other health benefits are out of scope.

Incorrect. There's no indication that the severity of skin cancer is related to exposure or prevention—it may be solely a factor of genetics.

Incorrect. The argument defines sunscreen lotions as being designed to block skin-cancer-causing UV radiation, so lotions that don't do this are out of scope.

Incorrect. The data here would be, in theory, possible to challenge by doing more studies. Evidence that is impossible to challenge usually takes the form of speculation, not hard numbers.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Studies show that those who use sunscreen develop as much skin cancer as those who don't, so they aren't effective.

Answer Anticipation:
This argument reaches an anti-causal conclusion—one thing doesn't cause another. This is based on a correlation and comparison—those who use the supposed cause (sunscreen) see just as much of a given effect (skin cancer) as those who don't. However, like most anti-causal conclusions on the LSAT, the comparison used to dispute the effectiveness of the cause is the wrong one. The reason is that there's reason to believe the group who uses the sunscreen is different from the other group—that group might be using more sunscreen because they're out in the sun more. The relevant comparison is between those who are in the sun for comparable times who use sunscreen and those who don't. The correct answer should highlight this problem.

Answer Explanation:
This answer highlights the common flaw in arguments that conclude, based on a correlation, that one thing doesn't cause another. If the group that uses sunscreen lotions is out in the sun much more frequently than the group that doesn't use these lotions, their cancer rate would be expected to be higher, so the fact that it's the same suggests that the lotion is working.

Key Takeaway:
Conclusions that a certain supposed cause doesn't have an intended or expected effect usually fall into the same pattern of not measuring against what the rate of the effect would have been without the cause. The answers usually highlight that the supposed cause shows up more frequently in cases where the given effect was more likely to begin with (e.g., traffic laws in an area with many auto accidents).