Agreement Between Birthplace and Self-reported Ethnicity in a Population-based Mammography Service

Background: Ethnicity is associated with genetic, environmental, lifestyle and social constructs. Difficult to define using a single variable, but strongly predictive of health outcomes and useful for planning healthcare services, it is often lacking in administrative databases, necessitating the use of a surrogate measure. A potential surrogate for ethnicity is birthplace. Our aim was to measure the agreement between birthplace and ethnicity among six major ethic groups as recorded at the population-based mammography service for British Columbia, Canada (BC). Methods: We used records from the most-recent visits of women attending the Screening Mammography Program of British Columbia to cross-tabulate women's birthplaces and self-reported ethnicities, and separately considered results for the time periods 1990-1999 and 2000-2006. In general, we combined countries according to the system adopted by the United Nations, and defined ethnic groups that correspond to the nation groups. The analysis considered birthplaces and corresponding ethnicities for South Asia, East/Southeast Asia, North Europe, South Europe, East Europe, West Europe and all other nations combined. We used the kappa statistic to measure the concordance between self-reported ethnicity and birthplace. Results: Except for the "Other" category, the most-common birthplace was East/Southeast Asia and the most-common ethnicity was East/Southeast Asian. The agreement between birthplace and self-reported ethnicity was poor overall, as evidenced by kappa scores of 0.22 in both 1990-1999 and 2000-2006. There was substantial agreement between ethnicity and birthplace for South Asians, excellent agreement for East/Southeast Asians, but poor agreement for Europeans. Conclusion: Birthplace can be used as a surrogate for ethnicity amongst people with South Asian and East/Southeast Asian ethnicity in BC.