Negative Effects of Race Mixing

A 1989 study stated that the risk of spouse homicide was 7.7 times higher in interracial marriages relative to intraracial marriages, that the risk for White wives was 12.4 times higher in interracial marriages, and that the risk for White husbands was 21.4 times higher in interracial marriages.

Source: https://web.archive.org/web/20200725190423/https://pubmed.ncbi.nlm.nih.gov/2705594/

A 2010 study stated that interracial couples had a higher risk for intimate partner violence, including intimate partner violence causing physical injury and/or arrest, than both ethnic minority and White couples.

Source: https://web.archive.org/web/20200725190548/https://journals.sagepub.com/doi/abs/10.1177/0886260509354510 

A 2005 study stated that Interracial marriage is associated with increases in severe distress for Native American men, white women, and for Hispanic men and women married to non-white spouses, compared to endogamous members of the same groups. Higher rates of distress are observed for intermarried persons with African American or Native American husbands or wives, and for women with Hispanic husbands.

Source: https://web.archive.org/web/20200725190828/https://www.sciencedirect.com/science/article/abs/pii/S0049089X05000438 

A 2008 study stated that Partners in interethnic unions generally reported lower levels of relationship quality than did partners in same-ethnic unions. These differences held for women as well as men, and for married as well as cohabiting couples. Differences in relationship quality were largely accounted for by more complex relationship histories, more heterogamous unions, fewer shared values and less support from parents. In contrast, differences in socioeconomic resources did not appear to play an explanatory role.

Source: https://web.archive.org/web/20200725191110/https://academic.oup.com/sf/article-abstract/87/2/825/2235473 

Mixed race/biracial individuals

The "National Household Survey on Drug Abuse" in 1999 stated that of the major racial/ethnic groups, drug use was highest among those reporting to be mixed race.

Source: https://web.archive.org/web/20200725191437/https://www.pbs.org/wgbh/pages/frontline/shows/drugs/buyers/whoare.html

A 2002 study stated that Mean levels of three characteristics—verbal IQ, number of sexual partners, and birth weight—were examined in African American, White (European-descent) Americans, and Black/White mixed race American adolescents. The sample came from Wave 1 of the National Longitudinal Study of Adolescent Health. The mean age was 16 years. According to their interviewers, the mixed race children had an African American physical appearance. The African American adolescents had a lower birth weight, a lower verbal IQ, and a higher number of sexual partners than did White adolescents. For each characteristic, the mixed race mean fell between the means of the two parental populations.

Source: https://web.archive.org/web/20200725191718/https://link.springer.com/article/10.1023/A:1016313718644?LI=true

A 2003 study stated that most earlier studies on mixed-race adolescents had found increased risk for emotional, health, and behavior problems. The most common suggested explanation was identity problems, leading to lack of self-esteem, social isolation, and family problems in mixed-race households. The study stated that it was the first using a large, nationally representative sample. Compared with non-mixed adolescents, the mixed race adolescents often had increased risk for various health problems, substance abuse problems, and behavior problems. While there were differences between different mixed race groups, there was a generally increased risk for all race combinations for most risks.

Source: https://web.archive.org/web/20200725191721/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1448064/

A 2006 study found increased risks for multiracial adolescents for various problems, including violent behaviours.

Source: https://web.archive.org/web/20200725191905/https://doi.apa.org/doiLanding?doi=10.1037%2F0002-9432.76.1.86

Another 2006 study which examined behavioral health found that multiracial Hispanics/Latino adolescents and multiracial non-Hispanic adolescents had more behavioral health problems than monoracial Hispanic adolescents.

Source:  https://web.archive.org/web/20200725192318/https://pubmed.ncbi.nlm.nih.gov/16528950/

A 2008 study stated that Over the past 40 years the fraction of mixed race black-white births has increased nearly nine-fold. [...] As one might expect, on a host of background and achievement characteristics, mixed race adolescents fall in between whites and blacks. When it comes to engaging in risky/anti-social adolescent behavior, however, mixed race adolescents are stark outliers compared to both blacks and whites. [...] Mixed race adolescents -- not having a natural peer group -- need to engage in more risky behaviors to be accepted.

Source: https://web.archive.org/web/20200725192126/https://www.nber.org/papers/w14192