A study of rescue workers after the 9.11 attacks on New York's World Trade Center shows the lowest rates of PTSD (6.2 percent) came from police who had been trained for the tasks they performed. According to a study in the American Journal of Psychiatry, volunteers and other workers (sanitation, construction, engineering) reported rates more than three times as high (21.2 percent). The number of hours worked and the length of shifts also influenced the trauma each experienced.
