Critical Reasoning

Over the past three decades, the number of hospital beds available for inpatient psychiatric treatment in the United States has declined from 4 per 1,000 population to 1.3 per 1,000 population. Over the same period in Japan, beds increased from 1 per 1,000 population to 2.9 per 1,000 population. Also during this period, annual mortality rates for persons with mental disorders have risen substantially in the United States, while declining in Japan.

Which of the following, if true, would cast the most serious doubt on the conclusion that the reduction in hospital beds is principally responsible for the increase in mortality in the United States?

(A) The number of hospital beds available for inpatient psychiatric treatment in Canada has declined over the past three decades, with no increase in mortality.
(B) Due to advances in medical care and training over the past three decades, outpatient treatment is more effective than inpatient treatment for many mental disorders.
(C) The incidence of mental disorders in Japan has been decreasing, even as the country has increased the number of beds available for inpatient psychiatric treatment.
(D) Over the past three decades, Japan has offered state-sponsored health insurance to all citizens, while the United States has not.
(E) Over the past three decades, the incidence of mental disorders that are more likely to end in death has risen in the United States and declined in Japan.

Source : Manhattan GMAT Foundations of Verbal, 6th Edition
OA=E

The first step in a critical reasoning problem is to read the question. This problem illustrates more even more clearly than others why this is so important. In this case the conclusion is contained in the question portion. If we don't read that, we won't have any idea what we need to do.

The logic of the argument is fairly straight forward. There has been an increase in mortality in the United States whereas mortality has declined in Japan. We also know that the number of beds has increased in Japan whereas the number of beds has declined in the US. The argument implies that the lack of beds is the cause of the increase in mortality.

However, we do not know that this change is the real cause. There could be many other causes. Perhaps the difference in diet is a factor. Perhaps there are genetic factors. There could be a number of reasons that would explain this difference that have nothing to do with the number of beds.

A is a possible answer. If the number of beds has declined in Canada without affecting mortality rate, this might be shown to weaken the causal relationship between number of beds and patient mortality. However, this number is not the same as the type of information we have been given in the problem. The problem shows number of beds per thousand population. Since answer choice A doesn't give this type of information, it should be considered a weak answer.
B provides irrelevant information. We are not interested in the difference between outpatient and inpatient care.
C provides us with more information, but since the conclusion is about the United States and not about Japan, this information doesn't seem that useful.
D is a possible answer because it offers another difference between care in Japan and in the United States. However, it requires us to speculate about the relationship between state-sponsored insurance and mortality rate. It's possible that many Americans have private health insurance or enough financial resources to pay for their own treatment. This should be considered a weak answer.
E is the best answer. It clearly suggests a cause for the increase in mortality that has nothing to do with the number of beds offered.