Question: When did individuals self-identify as belonging to a particular ethnic group?
Sentence: One is the system used in the 2001 Census when individuals identify themselves as belonging to a particular ethnic group: W1 (White-British), W2 (White-Irish), W9 (Any other white background); M1 (White and black Caribbean), M2 (White and black African), M3 (White and Asian), M9 (Any other mixed background); A1 (Asian-Indian), A2 (Asian-Pakistani), A3 (Asian-Bangladeshi), A9 (Any other Asian background); B1 (Black Caribbean), B2 (Black African), B3 (Any other black background); O1 (Chinese), O9 (Any other).
Answer in sentence: yes