not committed any serious security violations and who has settled into a social setting and learned many skills specific to his or her job, the costs to the government of putting that employee in some state of limbo involve training a replacement and perhaps damage to national security caused by the replacement of a valuable contributor with an inexperienced one. The costs to the employee include bad feelings, a waste of job-specific skills and knowledge, and perhaps a search for a new, probably inferior job. The costs to the government will be higher if there are negative side effects on morale or productivity of coworkers or on the ability to attract potentially productive employees.

The hardest estimate to make is the expected costs per undetected spy or terrorist. These will vary greatly by the potential of that person to do damage: from virtually none for ineffective spies to enormous amounts for successful ones who may compromise agents or give away invaluable technical information. A report on information collected on the 139 Americans who were officially charged with spying between 1940 and 1994 showed many to be low-level personnel who needed money and naively tried to sell some secrets (Taylor and Snow, 1997). Since 1978, 38 percent of spies caught were caught on their first attempt. In recent years, ideology has become much less important as a motive. Taylor and Snow (1997) credit the 1978 Foreign Intelligence Surveillance Act for both detecting and successfully prosecuting more spies than before. Despite the end of the cold war, foreign governments are still interested in U.S. secrets, with economic and nonmilitary technical information becoming relatively more important than they used to be.

The expected costs of an isolated security violation, such as taking classified information home, are the product of the value of that information to an adversary and the probability that the adversary gets it. Because many people with access to classified information slip up from time to time, it is fortunate that the probability of those mistakes leading to an important disclosure is quite small. This probability is hard to estimate, but the expected costs per violation might be approximated by dividing the costs of all leaks through inadvertent security violations (as opposed to espionage or hacking) by the number of such violations. An area with a very lax security system might attract attention from adversaries and increase the chance that any particular infraction there turns out badly.

For some purposes, it is useful to combine all the outcomes into one or two measures. In a cost-benefit analysis, all outcomes are replaced by an estimate of their dollar value, and if all outcomes but one are replaced by their dollar value, the one nonfinancial outcome is called the effect in a cost-effectiveness analysis. Typically in the health field, the effect is some measure of incremental health, such as years of life added. In employee screening, the effect would be undetected spies, so that the programs



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