(Mis)classification of ethnicity on the New Zealand Cancer Registry: 1981-2004.

Abstract

BACKGROUND: Māori and Pacific peoples are undercounted in cancer incidence statistics relative to census statistics. We use linked census and Cancer Registry data sets to determine the extent of misclassification between 1981 and 2004. METHODS: The 1981, 86, 91, 96 and 2001 censuses were anonymously and probabilistically linked to individuals with a cancer registration for the entire intercensal period, or 31 December 2004 in the 2001 cohort. We compared counts by ethnicity between census and Cancer Registry data. Correction ratios and percentage under or overcounts are presented. RESULTS: Undercounting of Māori and Pacific peoples was marked in the first cohort. For example Māori were under..