Nor would we think, in view of the obvious deterrent purpose of these searches, that the validity of the Government’s airport screening program necessarily turns on whether significant numbers of putative air pirates are actually discovered by the searches conducted under the program. In the 15 years the program has been in effect, more than 9.5 billion persons have been screened, and over 10 billion pieces of luggage have been inspected. See Federal Aviation Administration, Semiannual Report to Congress on the Effectiveness of The Civil Aviation Program (Nov. 1988) (Exhibit 6). By far the overwhelming majority of those persons who have been searched, like Customs employees who have been tested under the Service’s drug screening scheme, have proved entirely innocent – only 42,000 firearms have been detected during the same period. Ibid. When the Government’s interest lies in deterring highly hazardous conduct, a low incidence of such conduct, far from impugning the validity of the scheme for implementing this interest, is more logically viewed as a hallmark of success. See Bell v. Wolfish, 441 U. S. 520, 441 U. S. 559 (1979).