Doctor: Angiotensinogen is a protein in human blood. Typically, the higher a person's angiotensinogen levels are, the...

Carys on December 23, 2018

Flaw question

why is answer C correct, when another outside affect could contribute to an elevated BP?

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Ravi on December 23, 2018


Happy to help. You're exactly right—another outside effect could contribute to an elevated BP. You're pointing out a key problem of the argument by showing how the conclusion isn't necessarily true.

The stimulus tells us that angiotensinogen is a protein in human blood. The higher a person's angiotensinogen, the higher their blood pressure.

Inc. Angio - -correlated - -BP

We're also told that disease X causes an increase in angiotensinogen levels

X - -causes - -Inc. Angio

So now we have

X - -causes - -Inc. Angio - -correlated - -BP

The doctor then concludes that X is a cause of high blood pressure

X - -causes - -BP

Now, wait a second. This doesn't make sense, does it? Based on our map, we know that X causes inc. angio and inc. angio is correlated with BP. But we can't say that X causes BP from that. In order for the doctor's conclusion to work, we would have to assume that inc. angio causes higher BP, because that's the only way we can have a causal link from X to higher BP. This is the flaw of the argument.

Answer C states exactly the flaw we've found. C says that the argument illicitly infers, solely on the basis of two phenomena being correlated, that one causally contributes to the other. This is exactly what the doctor does in the argument. The doctor infers that since increased angiotensinogen is correlated with elevated blood pressure that an increase in angiotensinogen causes an increase in BP, which means X causes an increase in BP. This isn't necessarily true, and this is why the argument is flawed and C is the right answer.

Hope this helps. Let us know if you have more questions!