Logical reasoning PrepTest 153 · Section 3 · Question 17

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
A 12-year study of 1,000 middle-aged people found that those with lower blood levels of a particular nutrient found in fruits and veggies, called lycopene, were more than twice as likely as those with lots of lycopene in their blood to have a stroke. So, high lycopene must reduce the risk of stroke.

Answer Anticipation:
Remember, a causal conclusion is always vulnerable to attack. What are some other potential explanations for this correlation between low lycopene and high stroke risk? Maybe people who can't absorb lycopene from foods also have a higher stroke risk. Or people who eat lycopene-rich foods also exercise much more than those who don't, and exercise is already known to cut the risk of stroke in half.

Correct Answer:
Right up front. If eating a lot of lycopene also means eating a lot of other stuff that protects against stroke, then why is lycopene getting all the credit? It could just be a side effect of a diet rich in the other stroke preventive ingredients.

Key Takeaway:
When weakening a causal argument, always take a moment to think about alternate causes for the phenomenon alleged in the conclusion. Alternate cause answers are incredibly common in this LSAT category.

Incorrect. This strengthens the argument. It backs up the idea that lycopene causes a lower stroke risk by adding additional observations, presumably of a larger population.

Incorrect. Irrelevant. The study only dealt with middle-aged people, so its results shouldn't be affected by age-related changes in lycopene levels. It's apples to apples.

Incorrect. This makes sense given that lycopene comes from fruits and vegetables, but it doesn't weaken or strengthen the argument. It's just another fact.

Incorrect. This doesn't really matter. A wide variation doesn't make it harder or easier to measure lycopene levels or to figure out who had a stroke. Again, just an extra factoid.