BOSTON - A new risk calculator can predict an individual's risk of developing psychotic disorders such as schizophrenia, according to a new study published today in The American Journal of Psychiatry. The research involved collaborators from nine sites, including Beth Israel Deaconess Medical Center (BIDMC), and may help researchers test treatments to prevent onset of full psychosis.

Psychosis is characterized by hallucinations and delusions. The new calculator assesses an individual's risk of developing psychosis after experiencing early warning signs of schizophrenia, such as hearing voices.

"Until now, clinicians could give patients only a rough estimate of how their condition might progress--that some 15 to 25 percent of people who have experienced early warning symptoms will go on to develop a more serious disorder," said Larry J. Seidman, PhD, a psychologist at BIDMC and Professor of Psychology at Harvard Medical School. "With this new risk calculator, clinicians can now give patients an individualized assessment of risk. More precise information allows people to have a more realistic sense of what's going on, which can reduce anxiety."

In addition to stressful life events, trauma and family history of schizophrenia and, the calculator takes into account five other factors to determine an individual's level of risk. These factors include: age of onset of symptoms; levels of unusual thought content and suspiciousness; social functioning; verbal learning skills; and speed of mental processing.

Seidman and his colleagues analyzed data from interviews with 596 subjects, ages 12 to 35 years, who were diagnosed with Attenuated Psychosis Syndrome, a condition in which patients may experience hallucinations and/or develop unusual thoughts but recognize their perceptions aren't based in reality.

The research team, led by Yale University's Tyrone Cannon, PhD, then developed the risk calculator, which analyzes known risk factors for schizophrenia. After following up with the subjects every six months, the researchers found that 16 percent of the patients diagnosed with Attenuated Psychosis Syndrome had converted to psychosis within two years.

Symptoms of unusual thought content and suspiciousness contributed most to the risk of developing psychosis. A decline in social functioning, lower verbal learning and slower processing speed were also significant factors. People who were younger (in their teens or early twenties) when their symptoms began, were also at increased risk. Stressful life events, traumas and family history of schizophrenia turned out to have a lower impact on an individual's risk profile.

"The risk calculator does not take into account treatment or other potentially supportive environmental factors that may reduce risk; this is a direction for future research," Seidman said, adding that the power of the calculator lies in putting symptoms in perspective for patients and their families. "Having hallucinations, it turns out, doesn't add much predictive weight at all. Maybe this person has good cognitive function and has not declined socially--this profile would lead to a good score. Treatment can ensue, potentially with less fear."