Development of New Zealand's deprivation index (NZDep) and its uptake as a national policy tool.

OBJECTIVES: To outline the development and uses of the census-based New Zealand small-area index of relative socio-economic deprivation, NZDep.
METHODS: NZDep has been created from four 5-yearly censuses using theory developed from international deprivation research, a standard statistical procedure (principal component analysis) and both construct and criterion validation.
RESULTS: The latest index was based on nine socio-economic deprivation variables available for just over 4 million people. It was calculated from a basis of 24,000 small areas containing a median of approximately 90 people. The deprivation index has a value from 1 (low) to 10 (high). It is mapped to standard administrative areas and is available free of charge. The index is easy to visualize, and deprivation maps are widely used. The index is used in many applications in research and social epidemiology, and routinely by the country's Ministry of Health, both to explore health variations across the country and to allocate central government funds to local health care providers. Geographers in local government were quick to recognize the index as a good tool for visualizing the diversity and neediness of local communities, and hence as a tool for town and service planning.
CONCLUSION: The national NZDep index of small-area deprivation has been used widely in research on mortality, morbidity and determinants of ill health, and in needs assessment, resource allocation and advocacy.