Children who experience severe trauma are three times more likely to suffer from schizophrenia when they grow up, a new study suggests.

And the more severe the childhood trauma, the greater the risk of developing the mental illness, which affects people's emotional responses and ability to think logically, and in some cases, causes serious hallucinations.

"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," co-author Richard Bentall said.

The findings bring new light to the long-standing debate about nature versus nurture as it pertains to mental illness.

Most recent studies about psychotic disorders like schizophrenia, psychotic depression and bipolar disorder have tended to focus on the biological and genetic factors behind the diseases, the researchers note.

But this new evidence suggests biology alone isn't enough to fully understand these complicated disorders.

"Our findings suggest that studies on the neurological and genetic factors associated with these conditions, which are not yet fully understood, are more likely to advance our knowledge if we take into account a patient's life experiences," Bentall said.

"Now that we know environment is a major factor in psychosis and that there are direct links between specific experiences and symptoms of the condition, it is even more vital that psychiatric services routinely question patients about their life experience.

"Surprisingly, some psychiatric teams do not address these issues and only focus on treating a patient with medication."

The findings are based on data researchers at the University of Liverpool extracted from 27,000 research papers spanning 30 years that either address how children with trauma progress as adults, look at statistics from randomly selected members of the population or interview psychotic patients about their early childhood.