Our analysis shows that, when a neighbourhood becomes more diverse, it becomes less socially cohesive. This result is significant. Social-economic factors have been taken into account. Although the social-economic status of a neighbourhood impacts cohesion, the impact of diversity on social cohesion IS LARGER THAN THE IMPACT OF SOCIAL ECONOMIC STATUS.
From the summary (page 8):
In our investigation we checked three aspects of social cohesion: neighborhood cohesion, feeling of home, and social safety. We found the following:
Neighborhoods with high ethnic variety are considered less cohesive, less homely, less safe. Contrary to earlier research, we found that cohesion has a stronger relation with diversity than with socio-economic factors, like income and education level.
In municipalities with high ethnic diversity, more people have been convicted of criminal acts than low diverse municipalities. There's limit to this amount, meaning that moderately diverse areas (like Helmond or Gorinchem) have similar rates to highly diverse areas (like Den Haag or Rotterdam).
These relations are strongest among so-called 'middle-groups' (areas with similar populations of native and non-native).
I also came across a nice video explaining the facts on this phenomenon for those who wish to know:
