Coverage and accuracy of ethnicity data on three Asian ethnic groups in New Zealand

Objective: Detecting and eliminating ethnic disparities in access to and outcomes of healthcare relies on accurate ethnicity recording. Studies have shown that there are inaccuracies in ethnicity data in New Zealand and elsewhere. This study examined coverage and accuracy of ethnicity data for three Asian ethnic groups. Methods: Student researchers from, or with links to, the ethnic groups concerned worked with communities to recruit participants. Names and dates of birth, length of residence in New Zealand and immigration status were recorded. Names and dates of birth were sent to the New Zealand Health Information Service, which attempted to link them with National Health Index ethnicity data. Results: Only 72% of participants could be linked to an NHI number, and only 48% of those had their ethnicity recorded accurately. Linkage odds were lower for older people, and accuracy was higher for Chinese people compared to the other ethnicities. Length of residence and immigration status did not affect either coverage or accuracy. Conclusion: Most participants who could be linked had their ethnicity recorded in the broader category of "Asian", but accuracy was poor at the sub-group level. Implications: Extreme caution should be applied when examining data about subgroups within the 'Asian' category.