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Michael Butchard, MPH, 2014


Ischaemic heart disease (IHD) is the leading cause of health loss for Māori and the leading contributor to absolute health inequality between Māori and non-Māori. Revascularisation procedures (CABG and PCI) are best practice treatments for many clinical presentations of IHD, reducing morbidity and mortality, especially for acute presentations. From 1996-2000, Westbrooke and colleagues (2001) found that for selected cardiac interventions, national publicly funded rates for Māori were a third to a half those for Non-Māori. These findings are now over a decade out of date, and while there has been more recent research on cardiac revascularisation rate disparities by ethnicity, the Westbrooke and colleagues methodology has not since been repeated.


This study has three main aims; i) to calculate and compare the national publicly funded hospital discharge rates of cardiac revascularisations for Māori and non-Māori using a complete set of the most up-to-date hospital data and census populations; ii) to compare these results with the rates found by Westbrooke and colleagues (2001); and iii) to compare the results with rates of IHD (a proxy for need), and adjust results for comorbidities.


National Minimum Data Set (NMDS) hospital discharge data for the period 01/01/2009 to 31/12/2012 was used for the numerator. Denominator populations were derived from the 2006 Census. The R Project for Statistical Programming (R) was used to stratify numerator and denominator data by gender, ten-year age group from 25-84 years, deprivation (using the NZDep 2006 index census area units) and by Māori and non-Māori. Average annual rates for specific cardiac interventions, cardiac revascularisations (CABG and PCI), IHD, and IHD without comorbidities were plotted using R multi-panel graphs. Diagnoses and procedure codes were defined using ICD-10-AM 6th edition and AR-DRG version 3.1. Māori : non-Māori rate ratios were visually represented by multi-panel graphs and also numerically calculated. Revascularisation rate ratios were divided by the IHD rate ratios; and by 'IHD without comorbidities' rate ratios.


The main results were:i) Māori rates of revascularisations are generally higher than non-Māori for females of all ages and for males aged 45-64, but lower for all other male age groups; ii) after adjusting for need, Māori rates 4of cardiac revascularisations were lower than non-Māori rates (10-year age group revascularisation rate ratios divided by IHD rate ratios ranged from 0.59 to 0.83 for females and 0.58 to 0.74 for males); iii) after adjusting for comorbidities, the disparities reduced, but still remained (0.62 to 0.98 for females and 0.66 to 0.95 for males); iv) compared with Westbrooke and colleagues study, disparities have substantially reduced.


Māori compared to non-Māori rates of revascularisations have increased over the past 12 years; however, when compared to need, Māori rates are disproportionately low. This remains the case after adjusting for several comorbidities. While study limitations include the reliance on 2006 Census data, the results add to descriptions of disparities in New Zealand. Local and international literature suggests that patient clinical factors, physician bias, and hospital facilities could all potentially contribute to these disparities, as does the inequitable distribution by ethnicity of the social determinants of health.

Supervisors: Dr Phil Hider & Associate Professor Joanne Baxter

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