PrepTest 111

Incorrect. If anything, this weakens the argument by bringing up cases of Alzheimer's not caused by a virus, which would serve as counterexamples to the stimulus's conclusion.

Incorrect. The effects (symptoms) of the disease are out of scope—it's the cause that's relevant.50414,Incorrect. The argument isn't that both of these diseases have the same viral cause, just that both are caused by viruses. That said, if anything, by stating that the rat case is different from the human case (in that the virus that can't be the cause of Alzheimer's is to blame), this answer cuts against the argument.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Study - Blood from people with Alzheimer's was injected into rats, and those rats developed a disease like Alzheimer's. That other disease is caused by a virus.
Conclusion - Alzheimer's might be caused by a virus.

Answer Anticipation:
The argument here has two features that suggest specific flaws, and "fixing" those flaws is one way to strengthen an argument.

First, the argument features a study, and arguments that rely on studies tend to have sampling flaws, and correlation/causation flaws. For the sampling flaw, there were only 11 volunteers, but there could have been many more rats. And since the conclusion is very weak—"might/may be caused"—there doesn't need to be much support for it, so a sampling flaw is unlikely. For the correlations/causation flaw, the argument does feature a causal conclusion, but there is a causal premise as well—the other disease in the rats is caused by a virus. As such, there is the possibility of supporting a causal conclusion. That said, it doesn't do much to rule out alternative causes—in particular, maybe human blood all contains a virus that is harmless to them, but results in CJ disease in rats. Since there's no control group here, it's impossible to say, so establishing one could be a correct answer (rats that weren't injected with human blood and didn't develop the disease, or rats that were injected with human blood)

Second, and stemming straight from the last note, the argument relies on a comparison between rats and humans, and specifically between the disease seen in rats and Alzheimer's. However, there's no indication that rats and humans, or these diseases, are sufficiently similar to reach the conclusion that whatever caused the disease in rats is also possibly the cause of the human disease (Alzheimer's). As such, any answer that raises a relevant similarity between the two will serve to strengthen this argument.

Answer Explanation:
If the two diseases are actually the same disease, and it's known to be caused by a virus in rats, then it's very likely that it's also caused by a virus in humans. By bringing up a relevant similarity between the cases, this answer strengthens the argument based on the comparison.

Key Takeaway:
When an argument relies on two things being similar, then it can be strengthened by bringing up relevant similarities.

Incorrect. There could be any number of reasons that the blood of rats without the disease didn't cause CJ disease in other rats other than it's caused by a virus that wasn't present, so this answer is way too weak (in that it leaves open way too many possibilities) to affect the argument.