TVW Telethon Institute for Child Health Research, Centre for Child Health Research, Faculty of Medicine and Dentistry, The University of Western Australia, PO Box 855, West Perth, WA 6872, Australia.
There are significant implications for epidemiology, public health and social justice from the recent critiques of modern risk factor epidemiology by Susser and others. The need to move away from a focus at the proximal end of causal pathways and from single risk factors in individuals to looking at populations and the social and environmental contexts in which risk factors arise, points us more towards the social antecedents of diseases and other poor outcomes. In this paper I argue that we must pursue this broader agenda if we are to address the increasing burden of social morbidity in our communities, particularly amongst children and youth.
Susser's Critique of Modern Epidemiology
The need for a new era
The present era of epidemiology is coming to a close. The focus on risk factors at the individual levelthe hallmark of this erawill no longer serve. We need to be concerned equally with causal pathways at the societal level and with pathogenesis and causality at the molecular level.1
The recent criticisms of modern epidemiology19 stem from its focus on single risk factors in individuals and the tendency to ignore the social, behavioural and ecological contexts in which risk factors arise. Study after study describes the associations of many disease outcomes with social or economic factors and then proceeds to control for them in analyses that focus on more proximal risk factors in the causal pathway, some of which could be thought of as early signs of the disease. We have a myopic over-emphasis on proximal causes of disease and a concomitant neglect of upstream or distal factors that culminate in the final causal chain.3 This approach encourages a public health response which targets the individual to change behaviour, rather than targeting the societal situations which provide the environments in which risks arise.
Modern epidemiology also assumes that both risk factors and disease outcomes are static and dichotomous rather than evolving and distributed throughout the whole population. Many social risks operate across a continuum of intensity (dose) as well as varying throughout life. Population interventions that seek to modify mean population exposure may result in far greater reductions in poor outcomes than those which target individuals.10 We use sophisticated mathematical modelling to seek the independent effect of single risk factors and control for confounding, which frequently results in the important distal factors, which may be important in the causal path, being rejected from the model.11
Only recently have we started to realize that molecular and genetic science could be used to advantage to help elucidate these pathways, rather than be rejected as basic science and nothing to do with proper epidemiology or public health. In fact the elucidation of the code for the human genome and the explosion of genetic and biomedical research should actually encourage collaboration with epidemiologists.12 Whilst promises relate mostly to new treatments, the most exciting research that should emerge from this new knowledge is to investigate how genetic risks are modified by the social and physical environments in which we live, which may open up many more roads to effective interventions to improve public health. If epidemiologists do not participate in this process, it may not deliver the benefits in terms of improving population health.
Developmental Health and Well-being in Australia
These issues in epidemiology and public health are not just academic arguments.1315 They have enormous relevance to the response which we now urgently need to mount to counteract the effects of the rapidly changing social, biological and ecological environments in which we live. Over the last 30 years in Australia (and in many developed countries) we have observed increases in many major childhood disease categories and disabilities.16 These include mental health disorders, asthma and allergy, type 1 diabetes, neurological and developmental problems such as cerebral palsy, autism, and behavioural problems. (See ref. 16 for detailed references for each of these trends.) These increases are so substantial that the levels of morbidity can only really be tackled by preventive strategies as the health care and welfare systems cannot afford to meet the demand for treatments and services, and for many of these diseases there are no effective treatments.
Figure 1 shows the dramatic increases in young, particularly male, suicide rates in Australiathe rate for males has quadrupled and that for females has doubled over the last 30 years.16 The startling level of mental health morbidities in West Australian children is similar to that reported from Canada1719 (Table 1
)one in five teenagers has a mental health morbidity which interferes with their daily life. The increasing rate of cerebral palsy in very low birthweight infants (Figure 2
) as more and more of these tiny babies survive epitomizes the perinatal paradox,20,21 our obsession with keeping small babies alive and our dismal failure to prevent preterm births and disability in the wider community. Trends in preterm births are increasing16 and much of low birthweight and preterm birth arises in social adversity.2224 The major (and increasing) cause of post-neonatal cerebral palsy in Western Australia is now child abuse.11
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Changes in Australian Society The Great Disruption25
Table 2 lists the indicators of social functioning in our society which have changed dramatically over the last 30 years in Australia; changes which have occurred in many countries. These profound changes in population risk add complexity and a sense of urgency to our work. Changes in these social patterns have the potential to impact adversely on developmental health and well-being and do so in complex and interacting ways.
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Susser's new epidemiological paradigms and these increasing social problems in our societies have profoundly important implications for our research and prevention agendas. Our own research in Western Australia, as well as that from elsewhere, has shown that the social, community, family, biological and economic influences identified for many complex disease pathways appear similarly important in a range of other educational, psycho-social, behavioural and criminal outcomes.2628 Causal pathways thinking opens up the concept of multiple outcomes from single pathways and multiple pathways to single outcomes. Of course it also opens up new and more numerous preventive strategies, some of which, if acting early enough in the pathway, are far more effective and perhaps cheaper than those targeting later risk factors or early disease.11
Figure 3 shows the traditional risk factor thinking in the cause of cerebral palsy. Focusing on this birth asphyxia pathway has damaged obstetric care, as obstetricians have been sued for not delivering the perfect baby following the availability of new tools supposedly able to detect birth asphyxia and doing caesarean sections to reduce brain damage.11 As many have now shown, the causal pathways to the cerebral palsies are many, most commencing antenatally.11
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Simplistic causal paradigms which ignore the multi-level and complex nature of pathways, and policies and interventions which focus on a limited number of risk factors at some point along these pathways, are not going to serve us well.
Thus the implications for epidemiology are to acknowledge the complexity of causal pathways to a range of poor outcomes, investigate the social and ecological contexts in which causal pathways arise, develop better measures and analytical methodologies, create cross-disciplinary research collaborations with geneticists, psycho-social researchers, economists, sociologists and others, expand and link large population data bases to better serve a causal pathways approach and plan longitudinal studies carefully to enable multiple and interacting pathways to be studied. Figure 4 shows the new scientific tools we now have to improve epidemiological methods to better serve public health in this new era.
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Figure 5 shows the causal pathways to poor Indigenous health in Australia stemming originally from white colonization.34 The current risk factor approach focusing on individuals would be to target disempowered, marginalized, poorly educated and poor groups of mothers, to stop them smoking, to prevent low birthweight, ear disease and infections in their children. Such programmes fail, whereas those which attempt to strengthen the communities and the conditions in which they live tend to succeed.35 Success in preventing otitis media is extremely important in Indigenous communities as it is the beginning of another set of pathways to poor hearing, poor language and educational skills, low self-esteem, delinquency, substance abuse, unemployment, teen pregnancy and crime and thus poor adult social and physical health.36
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Research is currently done in silos, yet much research (methods, exposures, causal pathways and analysis) in these different disciplines is of enormous relevance to the causal pathways affecting outcomes of interest to those in other disciplines. Similarly policy and practice is developed in siloshealth, education, welfare, employment, justice, housing and family servicesand yet decisions made in each of these areas will have profound effects on the outcomes in development, health and well-being. Too few policies are evidence based, cost effective and for many of them we do not have the capacity to truly evaluate the impact of what we do. Australia is a small country (20 million people) with excellent well-funded public services and outstanding population data bases. We have established a major innovative Partnership for Development, Health and Well Being which will embrace the Bronfenbrenner ecological model of child development (Figure 6).36 In this model, the important influences of the larger social structures and economic, political and cultural environments on health and other outcomes are recognized. The impact of the apartheid regime in South African on black children's health, development and well-being is a powerful example of this.
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