Cognitive epidemiology: psychological and social risk mechanisms for psychosis

The hypothesis that psychosis exists in nature as a distribution of symptoms is not so bold as it may seem [1]. For example, in the case of depression, both genetic and community studies suggest that the phenotype is more likely to exist as a continuous (albeit skewed, [2]) distribution of symptoms rather than a true disease dichotomy [3-6]. Given the substantial degree of overlap in terms of psychopathology, outcome, risk factors and treatment between depression and psychosis [7], it is unlikely that psychosis, contrary to depression, would have a completely non-continuous, dichotomous distribution. Although possibly more skewed because of their lower prevalence, a degree of continuity in the distribution of symptoms would be expected. This hypothesis, however, has attracted relatively little research effort, especially from the psychiatric profession [8].