The validity of Maori hospital discharge statistics for ischaemic heart disease in New Zealand.

Data from an Auckland coronary heart disease register for the years 1983 to 1991 have been used to assess the validity of routine national statistics on Maori hospital discharge rates for ischaemic heart disease. Ethnicity as recorded on the hospital admission record was compared with self defined ethnicity as recorded by register interviewers. Unlike routine New Zealand mortality statistics, where there is marked underreporting of Maori mortality, it appears that hospital discharge statistics are not markedly affected by misclassification of ethnicity. Approximately 12% of those classified on the admission record as Maori considered themselves to be of a different ethnicity, and 0.5% of those classified as 'other' considered themselves to be Maori. Because of the small proportion of the population (and of ischaemic heart disease deaths) who are Maori, the two misclassifications cancel out and the overall routinely reported hospital morbidity rates are similar to rates based on self reported ethnicity. For example, in 1990, routine national statistics show that there were 345 Maori hospital discharges or deaths due to ischaemic heart disease, and 8946 events among other ethnic groups. After adjustment using the register figures to reflect self defined ethnicity, the figures were 347 and 8944 respectively.