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.

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.

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.

Childhood trauma is not necessarily a prophecy of doom, because some children are resilient or because later experiences help to restore mental health.

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.

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).