The incidence of psychotic disorders varies greatly across places and demographic groups

The distibution of negative and positive association data also varies according to geographical localisation and tends to cluster in hot and cold spots around the globe as shown here . Part of this is due to population genetics (polymorphisms have a single ancestral root and arise in a particular place at a particular time) . Some of this effect may also relate to the similarity between viral genes and susceptibility genes. In other words, some genetic studies have been tracking infection as well as identifying candidate genes.