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
The researcher’s conclusion depends on which of the following assumptions?
A. High immune-system activity protects against mental illness better than normal immune-system activity
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.
I picked C.I am not finding why c is wrong.Can u explain why c is wrong?
To tackle your doubt, let me begin from the passage itself.Understanding the PassageA 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.
This statement talks about a discovery by a researcher. The researcher discovered that people who have
low immune system activity have lower mental health
normal or high immune system activity have better mental health.
So, what he saw was that mental health increased with increase in 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 thought about the reason as to why this pattern exists. He thought an explanation for this pattern is that immune system protects against mental illness or poor mental health. If his explanation is true, then people with lower immune system should have poorer mental health than people with normal or higher immune system activity. This is what he has observed. So, he made the conclusion as stated in the above statement of the passage.Pre-thinking Assumption
Now, what is the assumption built in the conclusion drawn by the researcher?
The assumption is that there is no other explanation which could explain the given observed pattern. If there are other explanations for the observed pattern, then it would cast a serious doubt on the conclusion drawn by the author.
Now, what could be an alternate explanation?
This could be a hard question for people new to causal arguments but for people who have done some practice of causal arguments, they can figure out the answer to this quite easily.
Remember, the researchers concluded that immune system protects against mental illness because this can explain the observed pattern. Now, if we say that mental illness causes decline in immune system activity, then even this statement could explain the given observed pattern (where both immune system activity and mental health increase or decrease simultaneously). Now, if this could also be an explanation, then the author must have considered this explanation and 'assumed' that this cannot be be true.
So, an assumption in the above argument is that mental illness does not cause people’s immune-system activity to decrease. This is what option D is.
Now, coming to option C:
People with high immune-system activity cannot develop mental illness.
First of all, we need to think why does the author need to assume this? Remember a golden rule:
The author assumes only those things without which his argument will not hold true.
For this reason, the 'assumptions' are called must be true statements, which means that the assumptions must be true for the conclusion to hold true.
Now, is Option C a must be true statement?
What if option C is false i.e. People with high immune-system activity can develop mental illness. Will it falsify the conclusion?
The answer is No. The conclusion can still hold even when this statement is false. Therefore, it cannot be an assumption.
Hope this helps