“Schizophrenia has a hereditary component involving a combination of at least 10 genes. The presence of that combination increases the risk of this severe psychiatric disorder by 15-20%; the rest is down to external factors, one of the most important of which is being born in and growing up in a big city.”
Schizophrenia
Clarissa's Blog 
Interesting, though not surprising. A lot of questions, though. What’s considered a big city here? And how big of a contribution does city living make? And city living can’t be an independent variable here, can it – there are a lot of people living in big cities, after all, and an appreciable majority don’t have schizophrenia.
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If the research was done in America, growing up in a big city could have a correlation with ” growing up in poor neighborhoods in a big city”. That would explain the results.
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