Population Size Correlations
From the 2010 Census Brief “The Black Population” available online, we calculated the correlation between the number of reported African Americans living in a state and our sample of African Americans from that state. The correlation is strong, with p value of 9.5 × 10−14, suggesting that our low sample sizes from states in the US Mountain West is expected from estimates of population sizes.
African ancestry in European Americans most frequently occurs in individuals from states with high proportions of African Americans and is rare in states with few African Americans. This observation led us to look at the correlation between population size (as a percent of state population using self-reported ethnicity from the 2010 US Census) and state mean levels of ancestry.
To examine the interaction between proportions of minorities and ancestry, we used the 2010 US Census demographic survey by state. We compare the state population proportion to the mean estimated admixture proportion of individuals from that state, fitting linear regressions, and generating figures with geom_smooth(method = “lm,” formula = y ∼ x) from the ggplot2 package in R.
We find that African ancestry in European Americans is strongly correlated with the population proportion of African Americans in each state. We find that the higher the state proportion of African Americans, the more African ancestry is found in European Americans from that state, reflecting the complex interaction of genetic ancestry, historical admixture, culture, and self-identified ancestry.