Numerous psychological and sociocultural causes, such as disturbed family and interpersonal patterns, also have been proposed as possible causes. Schizophrenia has a higher incidence among lower socioeconomic groups, possibly related to downward social drift or lack of upward socioeconomic mobility, and to high stress levels, possibly induced by poverty, social failure, illness, and inadequate social resources. Gestational and birth complications, such as Rh factor incompatibility, prenatal exposure to influenza during the second trimester, and prenatal nutritional deficiencies, have been associated.