How large is the African American vs. European American gap in the United States?
There is consensus that there is a gap, but not consensus about its current size, with a range of estimates from about 8 to 15 IQ. Most sources reiterate the 15 IQ/1 standard deviation value.
Sources
Roth, P. L., Bevier, C. A., Bobko, P., Switzer, F. S., & Tyler, P. (2001). Ethnic group differences in cognitive ability in employment and educational settings: A meta‐analysis. Personnel Psychology, 54(2), 297-330.
The answer to the research question of “what are the standardized difference scores between ethnic groups?” is now clearer than the [generally accepted effect size] of “1.0 SD for Blacks versus Whites” and “somewhere between .5 and .8 SDs for Hispanics versus Whites.” If one simply examines the aggregate data and ignores the moderators, the overall ds for g are 1.10 for the Black-White difference and .72 for the Hispanic-White difference. However, there are a number of important moderators that merit discussion. We discuss the Black-White moderators first.
Sources
Neisser, U., Boodoo, G., Bouchard Jr, T. J., Boykin, A. W., Brody, N., Ceci, S. J., … & Urbina, S. (1996). Intelligence: Knowns and unknowns. American psychologist, 51(2), 77. Wikipedia page.