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

shunhe on August 6, 2020

Hi @hfatima1,

Thanks for the question! So let’s review this argument quickly. We’re told about angiotensinogen, a protein in human blood. Normally, the higher these levels are, the higher the person’s blood pressure is. And disease X usually causes an increase in these levels. So disease X must cause high blood pressure.

Now what does (D) tell us? It tells us that it confuses one phenomenon’s causing a second with the second phenomenon’s causing the first. In other words, it’s reversing the order of causation. So that would be like saying “having brown spots causes sunbathing,” when really, it’s sunbathing that causes having brown spots.

If (D) were true, then it would be the high blood pressure that causes disease X. But there’s nothing that indicates this in the passage. Rather, another problem should strike you as more obvious: the argument is mixing up correlation and causality, not messing up the direction of causality. It’s saying that higher angiotensinogen levels are correlated with having a higher blood pressure (since they both go up together). And the argument then concludes that since disease X causes an increase of angiotensinogen levels, it must also cause high blood pressure! But nothing indicates that the relationship is actually one of causation as opposed to correlation. So that’s the fundamental error here, and not reversing causality.

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