lheiannie07 wrote:Although the ratio of physicians to total population is about the same in the United States and Canada, the United States has 33 percent more surgeons per capita. Clearly, this is the reason people in the United States undergo 40 percent more operations per capita than do Canadians.

The explanation given above rests on an assumption that:

(A) patients in the United States do not have a greater need for surgery than do patients in Canada.
(B) the population of the United States is not larger than that of Canada.
(C) United States patients sometimes travel to Canada for certain kinds of surgery.
(D) General practitioners in the United States do not as a rule examine a patient who is a candidate for surgery before sending the patient to a surgeon.
(E) There are no unnecessary surgical operations performed in Canada.

What is wrong with option D?

OA A

Premise: The US has a higher ratio of surgeons per capita, and Americans undergo 40% more surgeries than Canadians.
Conclusion: In the US, the greater number of surgeries is due to the higher ratio of surgeons per capita.

Apply the NEGATION TEST.
When the correct answer is negated, the conclusion will be invalidated.

A, negated:
Patients in the United States have a greater need for surgery than do patients in Canada.
Here, US patients have a greater NEED for surgery, invalidating the conclusion that the greater number of surgeries is due to the higher ratio of surgeons per capita.
Since the negation of A invalidates the conclusion, A is an ASSUMPTION: a statement that MUST BE TRUE for the conclusion to hold.

The correct answer is A.

D, negated:
As a rule, general practitioners in the United States will examine a patient who is a candidate for surgery before sending that patient to a surgeon.
Since it is possible that general practitioners in Canada abide by the same rule, this negation does NOT invalidate the conclusion that the greater number of surgeries in the US is due to the higher ratio of surgeons per capita.
Eliminate D.