The above examples illustrate the complex of biologic, psychological, and social factors that result in a fitness for duty referral. Workplace needs set the tolerance limits within which the worker must operate. They are different for a police officer, for a correctional officer, for a schoolteacher, and for a school custodian. Tolerance limits are affected by factors out of the employer's control, e.g., civil service rules, union contracts, and by the culture of the workplace, the latter being a set of unwritten rules. Ideally, the psychiatrist who performs the fitness for duty examination would have all of the information described above, but in most cases does not. The psychiatrist who has this information can begin to put in place one part of the mosaic that is the ethnography of work.