Original ResearchHigher mortality in areas of lower socioeconomic position measured by a single index of deprivation in Japan
Introduction
As well as individual socioeconomic status such as social class, educational attainment and income, area characteristics have been focused on independent and critical determinants of population health.1, 2, 3 Previous studies showed that socially disadvantaged areas had higher mortality, morbidity and prevalence of health risk behaviour.4, 5, 6, 7, 8
Measurement of area socioeconomic condition, in particular, ‘deprivation’, is a critical matter in examining the relation between area characteristics and health. Deprivation is generally defined as a state of observable and demonstrable disadvantage related to the local community or the wider society or nation to which an individual, family or group belongs.9 Deprivation indices have a long history in the UK, where several traditional indices such as Townsend, Jarman and Carstairs have been developed and commonly used.10 This was followed by a number of studies for the development and use of deprivation indices in many countries including not only European countries but also Australia, Canada, New Zealand, the US, and others.11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 These indices were formulated at various administrative levels with multiple indicators mainly from census data, comprising multiple domains such as unemployment, low social class, low educational attainment, household overcrowding, and home ownership. These deprivation indices have been applied in funding formulas, resource allocation and research in a variety of settings such as health and other social services.16, 26
In Japan also, the relation between health level and area characteristics has been elucidated. Recent systematic studies using municipal data regarding all causes and cause-specific mortality along with several socioeconomic indicators showed significant relationships between regional mortality and socioeconomic characteristics.27, 28
There have been some efforts to formulate indices of area social characteristics in Japan, mainly representing wealth rather than deprivation, although these indices have not received consensus and are not used in epidemiologic and public health research.29 Instead of established indices, indices formulated from limited socioeconomic indicators using factorial analysis were used in previous studies, and a substantial relation between these indices and mortality was found.27, 30 However, the dimensions of socioeconomic disadvantage were not integrated into a single index, and the formulated indices appeared to represent not only socioeconomic disadvantage but also other area characteristics such as urban–rural difference.27, 28
Health inequalities in relation to socioeconomic factors have been of great interest in public health.31, 32 Examining health inequalities in Japan will provide important insights in this field, because the Japanese population shows the healthiest status in the world,33, 34 and it is suggested that relatively smaller socioeconomic disparities partly contributes to this excellent health level.35, 36 The development of an index representing socioeconomic disadvantage would stimulate the study of health inequalities in Japan. The present study formulated an index of area deprivation, which included critical domains of social disadvantage and was available for small area analyses, and examined the relation between the index and mortality at the levels of prefecture and municipality.
Section snippets
Units of analyses
The study units of this study were prefecture and municipality. Local public entities in Japan are divided into two categories: the first consists of municipalities (i.e. cities, towns and villages), while the second consists of prefectures. All districts in the country belong to one of the municipalities and fall within the boundaries of one of 47 prefectures. Tokyo prefecture (Tokyo Metropolis) includes 23 special wards (‘ku’) in addition to cities, towns and villages. Twelve large cities
Results
The age-adjusted mortality rate (per 100,000) of the 47 prefectures ranged from 579.4 to 756.1 for men and 286.9 to 347.7 for women in the total population, and 312.0 to 442.4 for men and 139.0 to 175.2 for women in the population aged under 75. The correlations between mortality and the original indicators in the deprivation index both for prefectural and municipal analyses are summarized in Appendix B.
The deprivation index calculated using the z-scoring method (DIz) by prefecture ranged from
Discussion
We formulated deprivation indices using multiple socioeconomic indicators at the prefectural and municipal levels in Japan, and examined the relation between the indices and mortality. The formulated deprivation indices were significantly related to higher mortality at both levels, especially for men and premature mortality.
Selection of indicators and the method of index formulation are critical matters in this study. Indicator selection was based on the main domains of established indices in
Acknowledgment
This study was supported by a Grant-in-Aid for Scientific Research by the Japan Society for the Promotion of Science (Grant nos. 14570326 and 16590497).
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