Often patients with ankle fractures that are stable, and thus do not require surgery, are given follow─up X─rays because their orthopedists are concerned about possibly having misjudged the stability of the fracture. When a number of follow─up X─rays were reviewed however, all the fractures that had initially been judged stable were found to have healed correctly. Moreover, these follow─up X─rays of patients of many different orthopedists working in several hospital were reviewed. Therefore, it is a waste of money to order follow─up X─rays of ankle fracture initially judged stable.In the argument given, the two boldfaced portions play which of the following roles?