There are two main hypotheses concerning the sociological causes of schizophrenia: the downward drift hypothesis and the social selection hypothesis. The downward drift hypothesis says that, given the level of functional impairment that occurs and is a necessary aspect for diagnosis, impairment will also occur in functional and occupational areas of life and lead to a downward drift in socioeconomic status (SES). Empirical studies that support this theory show that schizophrenic victims, differing from normal patterns, have a lower SES than their parents. The social selection hypothesis states that individuals who have a lower SES exist in environments that are more stressful--including aspects of life such as more crime, poverty, hunger, less education, and less nutrition--and are therefore more vulnerable to developing schizophrenia. Both of these hypotheses indicate that the development of schizophrenia is highly correlated with the level of stress in the individual's environment. Proof for this can be found in empirical evidence indicating that when the economic condition of a country is bad, a higher number of cases of schizophrenia is reported.