LSAT 152 | Section 2 | Logical Reasoning: Q18

LR Question 18 Explanation

QUESTION TEXT: Doctor: Angiotensinogen is a protein in human blood…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Disease X surely causes high blood pressure.

REASONING: Angiotensinogen levels are correlated with high blood pressure. Disease X raises angiotensinogen levels.

ANALYSIS: This argument mixes up correlation and causation. We know that angiotensinogen is associated with high blood pressure. But that doesn’t mean it is a cause. Whenever there is a correlation, there are four possibilities:

1. Angiotensinogen causes high blood pressure.
2. High blood pressure causes angiotensinogen.
3. A third factor causes both. E.g. maybe high blood sugar causes high blood pressure and also high angiotensinogen.
4. It’s a coincidence.

If #2 or #3 are true, it’s possible that disease X could raise angiotensinogen without raising blood pressure.

___________

1. This is a different flaw.
    
   Example of flaw: High blood pressure causes fatigue. So, if someone is tired, they will get high blood pressure.
2. This is a different flaw. You have to translate answers and fill in words from the stimulus. “A condition” = high angiotensinogen. “an effect” = high blood pressure.
    
   So this answer says the argument ignores this possibility: “Even if angiotensinogen levels cause high blood pressure, other factors may completely eliminate this effect and leave blood pressure no higher”.
    
   This….is not a flaw. Angiotensinogen still causes high blood pressure in this example! The fact that something is counteracted doesn’t mean it isn’t a cause.
    
   Example of flaw: I have been shot in the chest, while wearing a bulletproof vest. Bullets kill people, so I must be dead even though I am talking. Boo!
    
   (I am ignoring that the bulletproof vest can counteract the effect of a bullet, even though bullets do cause death normally)
3. CORRECT. See the analysis above. High blood pressure and angiotensinogen are correlated. The author incorrectly assumes that one causes the other. Sometimes a correlation is just random.
4. This answer describes getting causation backwards. It’s a different flaw.
    
   Example of flaw: If the cat eats the mouse, the mouse will die. So if the mouse dies, it will be eaten by the cat.
5. This is a different flaw, and rather complex. I’ve never seen any question use this as a correct answer. If it did happen, it would be a complex stimulus.
    
   Example of flaw: Shouting “RUN FOR YOUR LIFE!!” often causes a stampede, and this stampede may kill people. So, it is literally impossible for shouting “RUN FOR YOUR LIFE!!” to ever directly kill someone. (The argument ignores that startling someone with a weak heart may cause a fatal heart attack, or cause them to slip and fall to their death, or something like that.)

Recap: The question begins with “Doctor: Angiotensinogen is a protein in human blood”. It is a Flawed Reasoning question. Learn more about LSAT Flaw questions in our guide to LSAT Logical Reasoning question types.