Accurate diagnosis is the cornerstone of medical care. To plan a
successful treatment for a patient, a doctor must first
determine the nature of the illness. In most branches of
medicine, physicians can base their diagnoses on objective
tests: a doctor can examine x-rays to see if a bone is broken,
for example, or extract tissue samples to search for cancer
cells. But for some common and serious psychiatric disorders,
diagnoses are still based entirely on the patient's own report
of symptoms and the doctor's observations of the patient's
behavior. The human brain is so enormously complex that medical
researchers have not yet been able to devise definitive tests to
diagnose illnesses such as schizophrenia, autism, bipolar
disorder or major depression. Because psychiatrists must employ
subjective evaluations, they face the challenge of reliability:
how to ensure that two different doctors arrive at the same
diagnosis for the same patient. To address this concern, the
American Psychiatric Association in 1980 pub