Many studies show that incidence and prevalence rates of schizophrenia are related to the social characteristics of the patient's environment; hypotheses—such as that of social isolation—have been invoked to account for the association, but for the most part remain unconfirmed. That the symptoms of schizophrenia or that the clinical form of the illness may also be affected by environmental factors is less clearly established. Nevertheless, some interesting observations have been made, by Benedict and Jacks (1954) and by Yap (1951) for example. Sherman and Sherman's (1934) study of delusions in a mixed American population is probably the most detailed investigation of this kind. They found that American men formulated their grandiose delusions in terms of wealth; foreign-born males did so more often in terms of literary or artistic abilities; and in negroes a religious component tended to predominate. White women were less grandiose and more paranoid than men; but in negro women the reverse was found. Hallucinations were more common in women than in men, and far more common among negroes than whites. Somatic delusions were found more frequently in white than in negro families.