The alleles shared by the alleged father and child occur with different frequencies in people of different ethnic backgrounds. For example, some alleles are common in Chinese individuals but are less common in white European individuals and vice versa. Calculations of PI, CPI and probability of paternity depend on how common or rare the alleles shared by the alleged father and the child are compared to the general population.
Therefore, if we know the ethnic origin of the tested individuals we can calculate PI, CPI and probability of paternity more accurately.