The length of time patients stay in the hospital is determined less by their level of illness than by external factors such as funding. These factors vary from place to place, and may be different in private hospitals and public hospitals. For example, it is common for patients to stay 3 to 7 days in some private hospitals after a suicide attempt. The average length of stay at one hospital in New England is seven days when all patients are considered. The same patient with the same problem may end up spending three weeks in a public hospital in New York City. In many places, patients stay as long as their insurance will pay; this means that relatively priveleged patients (who have private insurance) have much briefer hospital stays than disadvantaged patients on Medicaid, because private insurance usually only pays for a certain, small, number of days of inpatient psychiatric care.
There are also factors internal to the hospital. In some hospitals, patients are required to work their way up a system of "levels" in which discharge is the final level. In that case the length of stay ends up being determined by factors such as whether the patient needs extra medication (this is an entirely artificial thing because patients are penalized for needing "extra" medication, but not if the doctor prescribes the required dose on a regular basis), whether they make their bed, and whether they participate in activities. This means that a patient who lies in bed all day reading great works of literature will be assigned a lower level that a patient who plays shuffleboard in the dayroom. And yet reading requires better mental health than any hospital activity I've ever run into. Activities tend to be designed for people of very limited intelligence. I've even heard that occupational therapists are taught to use the same activities for mentally ill people as for the developmentally disabled. Patients lose levels if they disagree with the staff or argue with another patient, even though normal people have disagreements all the time.
Lost in all of this are the needs of the patient. The questions which should be asked are "Can the patient manage on his/her own?", "Is the patient a suicide risk?", and "Is the person acutely psychotic?" Instead, discharge is planned according to insurance coverage or "behavior on the unit." Moreover, discharge planning, in the full sense, is ignored. Hospitals are supposed to make sure patients have somewhere to go when they get discharged and that they will receive appropriate follow-up care, but this is often neglected. I have seen hospitals discharge a homeless person on a Friday which guarantees they'll be on the street over the weekend. I have seen people who have no insurance and can't fill a prescription discharged without any medicine and a handfull of useless prescriptions. I have seen people discharged to crack houses or brothels. I have also seen people discharged who were completely unable to take care of themselves, who were highly manic, and who need residential care and can't arrange for it themselves. On the other hand, I have been in the hospital with people who are completely well and don't belong in a hospital under an involuntary commitment. In some hospitals, voluntary patients who give notice that they want to leave are immediately converted to involuntary status, so that no one is truly free to leave.
The length of stay and quality of discharge planning are completely divorced from the reality of the patients' illnesses. This is an issue to mobilize around. At a time when budgets are being cut, many people will get shorter and shorter stays. In places where the funding is secure, or even depends on how many patients a unit has ("the unit census") will keep people long after they should have been released.