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 researcherâ€™s 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 system.
(C) People with high immune-system activity cannot develop mental illness.
(D) Mental illness does not cause peopleâ€™s immune-system activity to decrease.
(E) Psychological treatment of mental illness is not as effective as is medical treatment.
The researcherâ€™s conclusion would be most seriously weakened if it were true that
(A) there was a one-year delay between the completion of a pilot study for the experiment and the initiation of the experiment itself
(B) peopleâ€™s levels of immune-system activity are not affected by their use of medications
(C) a few people with high immune-system activity had scores on the test of mental health that were similar to the scores of people who had normal immune-system activity
(D) people who have low immune-system activity tend to contract more viral infections than do people with normal or high immune-system activity
(E) high levels of stress first cause mental illness and then cause decreased immune-system activity in normal individuals