PrepTest 152, Section 2, Question 18
Doctor: Angiotensinogen is a protein in human blood.(35 more words not shown)
The doctor's argument is most(10 more words not shown)
- AIt confuses a(6 more words not shown)
- BIt overlooks the(25 more words not shown)
- CIt illicitly infers,(16 more words not shown)
- DIt confuses one(11 more words not shown)
- EIt takes for(32 more words not shown)
Reading the argument
Going together isn't the same as one causing the other. Higher levels of this protein tend to go with higher blood pressure, but why? Perhaps some other health condition raises both. Or perhaps high blood pressure causes the protein level to rise. Those are possibilities, not medical facts we've established.
Disease X does cause the protein level to rise; we can accept that premise. The missing step is what happens next. If the protein merely accompanies high blood pressure rather than causing it, increasing the protein doesn't automatically increase blood pressure. The doctor has joined a real causal link to a relationship that has only been observed.
What we’re looking for
The flaw answer should identify that unsupported move from the protein–blood pressure association to a causal connection.
Working the answers
- A
This would mean treating something required for an outcome as enough to produce it. The doctor hasn't established that this protein is required for high blood pressure and then mistaken that requirement for a guarantee. The evidence says the two tend to vary together. The error is assuming a cause from that association.
- B
This raises the possibility that another factor could cancel an effect. But the doctor's conclusion is that disease X is a cause of high blood pressure, not that every person with the disease must end up with high blood pressure despite all other influences. A factor can contribute to an outcome even when another factor counteracts it. More directly, the argument hasn't established the protein's causal contribution in the first place.
- CCorrect
The two correlated phenomena are the protein level and blood pressure. The doctor treats that correlation as evidence that increasing the protein increases blood pressure, then uses disease X's effect on the protein to reach the conclusion about the disease. The observed correlation doesn't establish that middle causal step.
- D
The opposite causal direction is a useful possibility to consider: perhaps blood pressure affects the protein. But this choice describes taking a known causal relationship and getting its direction backward. We haven't been given either direction as a fact. The established relationship between protein and pressure is only a correlation, which C describes accurately.
- E
The doctor never argues that disease X cannot cause high blood pressure directly. This choice describes ruling out a direct cause because an indirect route exists. Our doctor is trying to establish a causal route, and one of its links hasn't been shown. There is no further conclusion excluding all direct effects.
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