a variety of factors including budgetary constraints, the availability of existing staff, the experience of existing staff with interviewing techniques, and the number of candidates who respond to advertised positions. On the other hand, major municipal, state and federal law enforcement agencies may have a competitive waiting list for applicants and a lengthy and arduous hiring process that begins with a required minimum score on a written aptitude examination. Such tests may be given only a few times a year and the hiring process may last six to twelve months, with disqualification for cause a possibility at each of the steps along the way. These may include a credit history check, an exhaustive criminal and personal background check going back to age 16, psychological screening testing, polygraph exam, physical strength and agility testing, and a comprehensive interview panel. In some cases, even already certified peace officers are required to redo basic law enforcement training, either partly or in full, complete a three- to six-month field training program with a veteran field training officer, and accept twelve months of "at will" probationary employment that can result in termination for any or no reason. Officers with a history of moving from agency to agency, especially at short intervals, are closely scrutinized and often rejected as applicants in larger agencies for that very reason. Difficulty in obtaining employment does not always correlate with agency size, however, as some smaller agencies in affluent communities experience very little turnover. Causes Fragmentation The United States has a highly decentralized and fragmented system of law enforcement, with around 18,000 law enforcement agencies, and is regulated separately in the 50 states, plus US territories, the federal and local level as well. Hiring and disciplinary standards vary greatly between police departments, the majority of which are small in size. There is no national database of dismissed officers, who may or may not be de-certified to practice law enforcement by their jurisdictional regulatory agency, often called POST (Peace Officer Standards and Training) agencies, or by a similar agency. Some states have established a state-level database or taken other administrative measures to try to prevent dismissed officers from being rehired, but these databases are not centralized, nor do they have uniform prerequisites. The large population and land area of the country makes it further harder to notice these cases; an officer may have moved hundreds of miles away to join another