Surveys show a strong association between and schizophrenia.

The correct answer is smoking.
Many studies were conducted to try and prove the correlation between smoking and schizophrenia, and most of them gave the expected results - there is a relationship between the two. Most people who suffer from this disorder smoke - the reasons for this are various: since they are usually unemployed, they smoke as a way to relieve boredom or stress and anxiety, etc.