There is also evidence from epidemiological studies that psychotic-like experiences are much more common than has hitherto been thought (with about 10% of the population affected) and that these experiences exist on continua with healthy or 'normal' functioning: instead of the world falling into two groups (the psychotic and the non-psychotic) people vary in their disposition to psychosis and only a minority of people who have these experiences require or seek help.

At the population level, making the world more just and less unequal, while trying to figure out the toxic aspects of the urban environmental will probably help prevent a lot of psychosis.

Countries with the best-resourced medical services have the best outcomes for physical illness (it is better to have a heart attack in Washington or London than in rural Africa) whereas precisely the opposite is the case for mental illness (developing nations with limited psychiatric resources have better outcomes and lower suicide rates).

There are many kinds of adult adversities that can provoke severe psychological distress, including debt and unemployment, dysfunctional marital relationships and occupational stress. The reality is that the social causes of mental ill-health are all around us.

The only way you can estimate environmental influences is by measuring them.

My interest in the psychological roots of psychosis has both personal (my brother Andrew committed suicide) and professional origins (I was trained in a behaviorist approach to psychology which - whatever its limitations - at least taught me to see human behavior in its social context).

If we are to believe the evidence from clinical trials there are many effective pharmacological and psychological treatments for mental illness. Epidemiological data, on the other hand, says otherwise.