If you have a deep and abiding interest in this subject, then you should read the work of Harvard Professor Robert Putnum. Try to get ahold of the orginal academic studies if you can.
The article below is a summary of some of his work.
http://www.boston.com/news/globe/ideas/articles/2007/08/05/the_downside_of_diversity/
The article below is a summary of some of his work.
http://www.boston.com/news/globe/ideas/articles/2007/08/05/the_downside_of_diversity/