schizophrenia epidemology

Project description
Why the number of immigrants with mental illnesses such as schizophrenia are less than the original population in Saudi Arabia ?Most of the incidence studies( mostly in western countries)

regarding the epidemiology of schizophrenia,indicate that the number of people developing schizophrenia is more among immigrants than natives of the country. surprisingly, it was the

opposite in Saudi Arabia. after gathering data about schizophrenia (new cases) for two years (2009-2011) in Saudi Arabia it turned out that there were only 14 new cases of schizophrenia among

immigrant , compared with 435 new cases among Saudis
Please write an essay regarding this subject trying to explain this results ?