53．There is a great deal of geographical variation in the frequency of many surgical procedures—up to tenfold variation per hundred thousand people among different areas in the numbers of hysterectomies, prostatectomies, and tonsillectomies．
To support a conclusion that much of the variation is due to unnecessary surgical procedures，it would be most important to establish which of the following?
(A) A local board of review at each hospital examines the records of every operation to determine whether the surgical procedure was necessary．
(B) The variation is unrelated to factors (other than the surgical procedures themselves) that influence the incidence of diseases for which surgery might be considered．
(C) There are several categories of surgical procedure(other than hysterectomies， prostatectomies，and tonsillectomies)that are often performed unnecessarily．
(D) For certain surgical procedures．it is difficult to determine after the operation whether the procedures were necessary or whether alternative treatment would have succeeded．
(E) With respect to how often they are performed unnecessarily, hysterectomies，prostatectomies，and tonsillectomies are representative of surgical procedures in general．
答案：B
E为什么不对呢？E说h,p,t这三种情况是具有代表性的， 正好体现了统计类题目加强统计可靠性的原则。
B说variation是由于跟手术无关的原因靠成的。（这样可以说明variation是不必要的吗？我觉得这里的概念很模糊，请NN帮忙一下）
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