Logical reasoning PrepTest 137 · Section 4 · Question 18

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Birth-order effects aren't detected on standard personality tests, but they are reported by family members. So birth order doesn't affect personality, just perception of personality.

Answer Anticipation:
The Psychologist's argument concludes that something doesn't exist, though it's perceived to exist—so there are two parts to it.

That second part—that birth-order effects are perceived by family members—is supported by the information in the stimulus. A conclusion about what people perceive is validly drawn from a premise about those perceptions.

The first part, however, doesn't necessarily follow from the premise meant to prove it. That premise relies on the failure of something to show up on standard personality tests as establishing that it doesn't exist, but it never establishes that these tests would detect them if they exist. The correct answer, then, should establish that standard personality tests are the appropriate tests to look for birth-order effects—in other words, these tests would detect them if they existed.

Answer Explanation:
This answer establishes that the standard personality tests would detect these birth-order effects if they existed—in other words, if these tests don't detect them, they don't exist. That's the assumption of the argument, so this is our answer.

Key Takeaway:
Whenever an argument relies on a proxy to reach a conclusion—a test or other measurement—be sure that it establishes it as the relevant way to reach the conclusion. Without specifically noting that the test is appropriate or certain, the conclusion is flawed.

Incorrect. If anything, this undercuts the argument by suggesting that the birth-order effects witnessed by family members are real, and the person was acting differently when undergoing the standard personality test.

Incorrect. Perceptions can change but still include birth-order effects. Maybe only other aspects of the personality are perceived to have changed, or the perception changes from one birth-order effect to another.

Incorrect. Since the argument relies on these tests not detecting birth-order effects, this answer isn't necessary in reaching that conclusion. This is trying to get you to pick it because the argument talks about "lasting" effects, but it says that there are no lasting effects, which could mean they didn't even exist to begin with.

Incorrect. The argument brings up effects that don't exist but are noticed by family members, so it relies on parent/sibling perceptions not being accurate.