Psychologist: Birth–order effects, the alleged effects of when one was born relative to the births of siblings, have ...

shunhe on July 13, 2020

Hi @kbernard,

Thanks for the question! So let’s take a look at what this stimulus is telling us. We’re told that birth-order effects (which are supposed to be effects that happen based on what order you’re born in relative to siblings, like if you’re oldest versus youngest) haven’t been detected in standard personality tests that are supposed to find it in adult personality. But these effects have been detected in birth, since parents and siblings report differences. The argument then concludes that taken together, the studies show that birth order doesn’t have a lasting effect on personality; instead, the order of birth just affects how your behavior is perceived, and not how you actually end up behaving.

So now we’re asked for an assumption required by the psychologist’s argument. Let’s take a look at (A), which tells us that standard personality tests will detected at least some birth-order effects on personality, if those effects exist. And clearly, this is something that’s going to be assumed by the passage. We can test this out by negating it. Let’s say that (A) isn’t true; that standard personality tests won’t detect any birth-order effects on personality, if those effects exist. Well, then it’s possible that there were effects on personality (as shown by the reports by parents and siblings) that just weren’t picked up by the standard personality tests. And that would mean that birth order does have a lasting effect on personality, which is the opposite of what the author concludes. So if (A) is wrong, the argument falls apart, and so (A) is a necessary assumption of the argument.

Hope this helps! Feel free to ask any other questions that you might have.