Critical Reasoning

A researcher discovered that people who have low levels of immune system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity. The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical disease.

The researcher conclusion depends on which of the following assumptions?

(A) High immune-system activity protects against mental illness better than normal immune-system activity does.
(B) Mental illness is similar to physical disease in its effects on body systems.
(C) People with high immune-system activity cannot develop mental illness.
(D) Mental illness does not cause people's immune-system activity to decrease.
(E) Psychological treatment of mental illness is not as effective as is medical treatment.




Please explain the options

This is an example of misplaced cause and effect

Low Immune --> Low mental health.


The assumption that must be true is that low mental health does not actually cause the low immune system activity. i.e. Low mental health --> Low immune activity.


If it is the later, then the immune activity is not the cause as the researcher concluded.

That is the reasoning for Answer choice D.


A) Keep in mind that we are relating low to normal or high, not normal to high
B) There is no reason it has to be similar for the immune system to be able to counteract affects
C) This is a bit too strong
D) See above
E) The passage doesn't address this at all.

Jim

If you apply negation test to C then it completely destroys the conclusion

People with high immune-system activity CAN develop mental illness. Here, it should be C


If you apply negation test to D it becomes

Mental illness DOES cause people's immune-system activity to decrease.

Here it is irrelavant bcuz we are looking at low immunity caused due to mental illness not vice versa...

Please explain

src_saurav wrote:Jim

If you apply negation test to C then it completely destroys the conclusion

People with high immune-system activity CAN develop mental illness. Here, it should be C

You are missing some key words. In the passage it says people 'TEND to score much lower....' Not all do.

In C, just because people (maybe not all, but 1, 2 or a few) with high immune-system activity CAN develop mental illness, doesn't mean the immune system does not protect against it.

src_saurav wrote: If you apply negation test to D it becomes

Mental illness DOES cause people's immune-system activity to decrease.

Here it is irrelavant bcuz we are looking at low immunity caused due to mental illness not vice versa...

This is the exact point. It is the opposite of irrelevant. If mental-illness is what causes immune activity to be high or low, we CANNOT say that it is the other way around - it is faulty logic.