The upcoming paper "The Decline of Brussels: Immigration and social inequality in Belgium" has devastating data about the effect of North African populations on Belgium's social indicators. The chart in pic related shows something called the "S"-factor, which is a general indicator of inequality, income mobility, and other social trends. Belgium's S-factor declines SHARPLY in areas with more North Africans.
The data/methodology for the study is already available:
http://rstudio-pubs-static.s3.amazonaws.com/290844_e95c33f807984afb9f94efc706cddf76.html
I know this stuff seems obvious to us, but academics are usually afraid to study it and produce proper academic work on these subjects.