Weaken (Over the past three decades, the number of hospital)

[ZiYuen]

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

I am not convincing that (E) will weaken the argument since death toll for mental disorders is on the rise in US.

Conclusion : Annual mortality rates for persons with mental disorders have RISEN substantially in the United States, while declining in Japan.

(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.

[RonPurewal]

the ARGUMENT blames the reduction in hospital beds for the increase in deaths.

according to choice E, though, more people (proportionally) in the US have had mental disorders that tend to be deadly.
if this is true, then, mortality should rise EVEN IF THERE'S NO CHANGE IN THE NUMBER OF HOSPITAL BEDS. in other words, it's less likely that the reduction in hospital beds is the cause.