LSAT 90 - Section 2 - Question 15

This is a Strengthen question.

The psychologist starts by defining jargon. “Cognitive plasticity” is the willingness to accept new ideas. Then we’re told the results of a study which found that cognitive plasticity (negatively) correlates with birth order. That means that firstborn children tend to have lower cognitive plasticity than last-born children. Or in other words, later-born children are higher in cognitive plasticity.

The next premise is also a correlation but the psychologist simply declares it to be “reasonable.” For analyzing the argument, we’ll simply treat this second premise as true, because it's a premise. Cognitive plasticity is positively correlated with adventurousness.

So now with the two correlational premises we have a correlation chain. Birth order is correlated with cognitive plasticity which is correlated with adventurousness.

The psychologist concludes with a prediction. She says that birth order will be negatively correlated with adventurousness. That means that firstborn children will tend to be less adventurous than later-born children. Or in other words, later-born children will tend to be more adventurous than their eldest siblings.

As is typically the case with Weaken and Strengthen questions that utilize causation logic, it's hard to anticipate where the answers will go. This is why we default to the strategy of POE. The strategy works pretty well here.

Answer Choice (A) says some of the great creative geniuses in history were firstborn children. We can write this answer off simply for being unrepresentative. The correlations in the premises and conclusion are about people in general. (A) confines itself to great creative geniuses in history. We should be very hesitant to draw any inferences from those people because by definition they are unrepresentative of the general population. Additionally, even if we were to draw some inferences from this unrepresentative sample, it pushes in the wrong direction. Firstborn children are supposed to be less adventurous.

Answer Choice (B) says, in most cases, the more younger siblings one has, the greater one's cognitive plasticity. This is a comparative statement so let’s make sure we understand what is being compared. On the surface it sounds like it's contradicting the correlation above. But that's not true. The correlation above compared cognitive plasticity of siblings to each other. (B) compares the cognitive plasticity of firstborn children to other firstborn children. (B) is comparing people who are not each other's siblings. According to (B), the eldest of five siblings from one family will tend to be more plastic than the eldest of two siblings from another family. Now that we know what (B) is saying, we can eliminate (B) for being irrelevant. Imagine if (B) stated the opposite, that the eldest of five siblings is less plastic than the eldest of two siblings. So what?

Correct Answer Choice (C) says other studies have shown a correlation between cognitive plasticity and the willingness to take risks. This is helpful for the argument because it reveals another correlation (backed up by studies) which suggests a causal mechanism. Now that we know cognitive plasticity correlates with risk-taking, a plausible hypothesis arises which can explain why birth order might correlate with adventurousness. It's because birth order correlates with risk-taking and risk-taking is what causes one to be adventurous.

Answer Choice (D) says a study of business executives shows that several industry leaders have older siblings. This is similar to (A) in that we should be careful about drawing inferences about the population at large based on the sample here which reveals information about only several people. Several people who happen to be industry-leading business executives have older siblings. This should be entirely unsurprising. I'm sure it's also true (even though (D) doesn't say it) that several people who happen to be industry-leading business executives have younger siblings or are the middle child or are the only child. But whatever information is revealed about whether or not they have siblings or the birth order they inhabit, there are just too few of them for us to use this information in a reliable manner. Another issue is the questionable relationship between being a business executive and being adventurous. I'm not sure which way that assumption goes. Are you more likely to be a business leader if you're more adventurous? Perhaps that's true. But the need to make this assumption is also a weakness of this answer choice.

Answer Choice (E) says most participants in the study had characterized themselves as more adaptable than other people. We can eliminate this answer simply by recognizing that it’s not clear what the relationship is between being more adaptable and being adventurous on the one hand and birth order on the other.