This document is a comprehensive index of studies, both historic and contemporary, detailing the negative effects of racial and ethnic diversity. The authors of these studies hold a wide range of political beliefs, though, pro-diversity/globalism, pro-left-wing/liberal are the most common among them.
This data statistically validates, beyond all reasonable doubt, the theory that racial and ethnic diversity is overwhelmingly negative. Diversity is colossally detrimental to individuals and society alike, in almost every conceivable way: physical and mental health, social cohesion,
violence, trust, criminality, etc.
The more diverse a society is, the more pronounced and severe these negative effects are, however, even small amounts of racial or ethnic diversity are enough to cause a quantifiable negative impact. Individuals of every race fare worse within racially and ethnically heterogeneous societies, though racial heterogeneity has a greater negative impact than ethnic heterogeneity (when the ethnically heterogeneous society is mono-racial).