London: Children who have undergone severe trauma are thrice as likely to develop schizophrenia in later life, says a new study. Previous research focused on the biological factors behind schizophrenia, bipolar and psychotic depression, but more evidence is now surfacing to suggest they cannot be fully understood without examining experiences of individual patients.

Richard Bentall, professor at Liverpool's Institute of Psychology, Health and Society, who led the study, said: "The causes of psychotic disorders, particularly schizophrenia, are a source of controversy amongst psychiatrists, psychologists and doctors.

"There is also disagreement about how the disorders are defined. It's not unusual, for example, for a patient to be diagnosed with schizophrenia by one psychiatrist, but as bipolar by another," he added, the journal Schizophrenia Bulletin reports.

The study, conducted by teams at Liverpool and Maastricht University, Netherlands, looked at more than 27,000 research papers produced over 30 years, to extract data from three types of studies, according to a Liverpool statement.

They are those that address the progress of children who have experienced adversity; studies of randomly selected members of the population; and research on psychotic patients who were asked about their early childhood.

Across all three types of studies the results led to similar conclusions. Children who had experienced any type of trauma before 16 years were approximately three times more likely to become psychotic in adulthood compared to those selected randomly from the population.

Those that were severely traumatised as children were at a greater risk, in some cases up to 50 times increased risk, than those who experienced trauma to a lesser extent.

Childhood sexual abuse, for example, was tied with hallucinations, whilst being brought up in a children's home was linked with paranoia.