Original researchCross-national injury mortality differentials by income level: The possible role of age and ageing
Introduction
Over the last centuries, most countries, developed and developing, have seen dramatic epidemiologic and demographic changes; mortality and fertility have declined enormously, the population has grown and disease patterns have shifted. These major changes led to the formulation of two theories: demographic and epidemiologic transition theories. Later, the term ‘health transition’ was suggested to encompass the related theories of demographic and epidemiologic transition, and to extend the theories further to encompass the economic, social and cultural aspects of development that drive these shifts in population and health.1, 2, 3 The demographic transition theory explains the population growth in terms of a process in which there is a transition from a stage with high mortality and fertility rates to a stage with low mortality and fertility rates.4, 5 The demographic component refers to the ageing of populations as a result of declining fertility and declining death rates, particularly in children.
According to the health (epidemiologic) transition theory,6, 7 as the risk of dying from communicable diseases is reduced for a population, those saved from dying from such causes survive into middle and older ages where they face elevated risk of dying from degenerative and man-made diseases. Since degenerative diseases tend to kill at much older ages than infectious diseases, this transition in causes of death is characterized generally by a redistribution of deaths from the young to the old. Further changes in the mortality profile have been associated with a proposed advanced stage of the transition ‘Age of delayed degenerative diseases’ by Olshansky8 and Ault, which they see as a stage that will propel life expectancy into, and perhaps beyond, the ninth decade.
The health transition theory remains a useful framework for the understanding of changing patterns of mortality and health. Nevertheless, little is said about injury in relation to health transition theory. Most analysis and attention is focused on historical shifts from communicable to non-communicable disease patterns. Recent cross-sectional studies on injury in a health transition perspective, however, suggest that economic development may play a fundamental role as a driver of changing patterns of injury mortality.9, 10, 11, 12, 13, 14, 15 The strength and direction of the association vary considerably with age, sex and type of injury. For example, when analysing national cause-specific injury mortality rates by gross national product (GNP) per capita, unintentional injury mortality (UIM) rates correlated negatively with GNP per capita for all age groups except 75+ years.9, 10, 11, 12, 14 In a similar study on homicide, there was clear negative association between homicide rates and GNP per capita among all age groups except for 1–4 years, where a weak positive association between homicide and GNP per capita was found.15 Suicide increased slightly in association with nation's income per capita, especially among women.13
Consequently, studies on economic level and injury mortality show complex and deviating associations where demographic transition might serve as a mediating and explanatory link. This study aimed to examine age- and cause-specific injury mortality differentials between low-income (LICs), middle-income (MICs) and high-income countries (HICs), and to discuss their implications in explaining changing injury mortality patterns with economic development against the background of general health transition theory.
Section snippets
Data sources and inclusion criteria
The World Health Organization's (WHO) mortality database for the year 2000 was used as the source of age- and sex-specific injury mortality data.16 These statistics provide archival information on numbers of deaths (numerator data) by age, sex and cause, as well as population estimates (denominator data) for all regions of the world. Data for all countries reporting to the WHO mortality database were reviewed. Some countries were excluded due to small population size (<1 million) in order to
Results
Fig. 1 illustrates the injury mortality rates for UIM, suicide and homicide by age- and income-based groups in the 66 countries. In LICs and MICs, UIM rates increased with age between 5–64 years and in HICs between 5–24 years. The rates in HICs plateaued with age but then increased among older populations. The highest UIM rates were seen among elderly populations in HICs. It is noteworthy that for adults aged 15–64 years, UIM rates were highest in MICs, while in children aged 0–4 years, LICs
Discussion
This was an explorative study that did not aim to determine causal mechanisms between age-related injuries and economic development; therefore, the scope of the study is limited to specific relationships between these variables. This study on injury mortality by country's income level is part of a broader research programme on economic development as a determinant of injury mortality.13, 14, 15 Findings in this study are mainly in line with those of earlier studies dealing with national
Conclusion
Age largely determines whether a certain injury category is seen as a ‘disease of poverty’ or a ‘disease of affluence’. While unintentional injury in children and homicide (all ages) appear to be ‘diseases of poverty’, unintentional injury among elderly people and suicide (especially in women) appear to be ‘diseases of affluence’. Moreover, for the adult population, UIM rates peak for MICs, possibly pointing to a third intermediate and transitory stage, here tentatively denoted ‘disease of
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