"This research highlights the significance of social disadvantage as a cause of severe mental illness. Our study found that UK African-Caribbeans who had been separated from one or both parents for 4 years or more during childhood were more likely to develop schizophrenia. A similar link was also seen with unemployment in British Afro-Caribbeans.

"Early studies by others indicated extremely high rates of schizophrenia in African-Caribbeans in the UK compared to the white population. Our work began in 1991 and we found that twice as many African-Caribbeans developed schizophrenia compared to white people with the similar backgrounds. We then went on to find out why this was the case.

"We first made sure that this finding wasn't simply due tohigher incidence rates among the population in the Caribbean by conducting studies in Trinidad and Barbados. We found the rate of schizophrenia there significantly lower than in London's African-Caribbeans, suggesting that social and environmental factors were responsible for the high UK rates.

"It's important we find out why this disease is more prevalent in this ethnic group, not least because of the distress it causes to patients and relatives in this disadvantaged section of the population. The knock-on effect of the increased rate is a greater strain on psychiatric services in London and inner city hospitals. Plus, on another level, finding out the cause of the disease in African-Caribbeans will help us to understand it better in all populations, because it is clear that schizophrenia isn't just down to poor genetics or neuro-developmental patterns."