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?

【选项】For certain surgical procedures.it is difficult to determine after the operation whether the procedures were necessary or whether alternative treatment would have succeeded.