NZiDep: a New Zealand index of socioeconomic deprivation for individuals.

The aim of this research was to identify a small set of indicators of an individual's deprivation that is appropriate for all ethnic groups and can be combined into a single and simple index of individual socioeconomic deprivation in New Zealand. The NZiDep index of socioeconomic deprivation was derived using the same theoretical basis as the national census-based small-area indices of relative socioeconomic deprivation. The index has been created and validated from the analysis of representative sample survey data obtained from approximately 300 Maori, 300 Pacific, and 300 non-Maori, non-Pacific adults. Twenty-eight deprivation-related characteristics, derived from New Zealand and overseas surveys, were analysed by standard statistical techniques (factor analysis, Cronbach's coefficient alpha, item-total correlations, principal component analysis). The index was validated using information on tobacco smoking, which is known to be strongly related to deprivation. The NZiDep index is based on eight simple questions which take 2-3 min to administer. The index is a significant new (non-occupational) tool for measuring socioeconomic position for individuals. We argue that the index has advantages over existing measures, including a specific focus on deficits, applicability to all adults (not just the economically active), and usefulness for all ethnic groups. Its strengths include focus, simplicity, utility, acceptability across ethnic groups, construct validity, statistical validity, criterion validity (measured with reference to tobacco smoking), and relevance to the current New Zealand context. The index is indicative of deprivation in general, and is designed for use as a variable in research, and for elucidating the relationships between socioeconomic position and health/social outcomes.