process, they contend, reduces the competitive pressures on hospitals, resulting in low salaries and long, unsafe work hours. The National Resident Matching Program has also been accused of deliberately limiting the available residency posts, thus decreasing the demand for residents, despite work for many more residents being available. In emergencies and in chronically understaffed health systems, all staff, including junior doctors, may be overworked. In some cases, excess work may be disproportionately assigned to junior doctors. There are financial incentives for overworking junior doctors. Since the least-experienced staff are usually paid less, it is cheaper to assign paid overtime to them. Deliberate understaffing and paid or unpaid overtime for junior doctors is thus used to reduce costs for medical facilities, although this may also reduce quality of care, which can be expensive. The medical culture has also been blamed. "Generation-bashing", where senior doctors look down on junior doctors who work fewer residency hours than they did, can push junior doctors to overwork. A desire for formal recognition, such as promotion, may also be important. A higher "entry barrier", with work conditions poor enough to burn out some residents, may be actively desired. There is also a belief that long hours do, or can, improve training. The ability to follow a patient from admission through the next 30 or 40 hours may be valued more than observing several patients for shorter periods. The desire to continue caring for a patient frequently leads doctors to work for longer than is permitted. Effects on health Effects of sleep deprivation on residents The evidence for harm to people who are deprived of sleep, or work irregular hours, is robust. Research from Europe and the United States on nonstandard work hours and sleep deprivation found that late-hour workers are subject to higher risks of gastrointestinal disorders, cardiovascular disease, breast cancer, miscarriage, preterm birth, and low birth weight of their newborns. It has also been shown that slow-wave sleep assists in clearing out toxins that build up during the day. Consequently, the disruption of slow-wave sleep increases the level of amyloid-beta, a protein aggregate commonly found in Alzheimer's, present in cerebrospinal fluid the following morning. Chronic sleep deprivation and the resulting fatigue and stress can affect job productivity and the incidence of workplace accidents. There are also social effects. Married fathers in the United States who work fixed night shifts are 6 times more likely than