These three papers can give you a sense of the epistemological and methodological issues involved in counting, labeling, and classifying "ethnic minorities" within and across countries:
Bhopal, R. and Donaldson, L., 1998. White, European, Western, Caucasian, or what? Inappropriate labeling in research on race, ethnicity, and health. American journal of public health, 88(9), pp.1303-1307.
Senior, P.A. and Bhopal, R., 1994. Ethnicity as a variable in epidemiological research. BMJ: British Medical Journal, 309(6950), p.327.
Feskens, R., Hox, J., Lensvelt-Mulders, G. and Schmeets, H., 2006. Collecting data among ethnic minorities in an international perspective. Field methods, 18(3), pp.284-304.