The need for an evidence base - Evidence based Public Health.
This session aims to help you apply knowledge and understanding to the methods of obtaining evidence that underpin Public Health. You should be able to:
- develop an understanding of the 'population approach' and the main methods of measuring the health of a population
- assess the ways in which interventions can be introduced to reduce the burden of illness
- discuss the barriers to the introduction of an evidence base to the practice of Public Health
We are probably all familiar with the notion of 'Evidence-Based Medicine', EBM, the term having been expanded to Evidence-Based Practice to go beyond clinical practice. An evidence base for Public Health is as important as it is for individual patient care in clinical practice - in fact probably more so since a Public Health policy may affect many thousands of individuals. One of the main differences is that it is much easier to design and undertake a randomised controlled drug trial amongst patients (in fact EBM has been termed Pharmaceutical Based Medicine as so much of EBM deals with pharmaceutical agents), than it is to design high quality research into population-based interventions and collect evidence. Here are some links to resources which discuss this issue in some detail.
Need for Evidence Based Practice
From Evidence-based Medicine to Evidence-Based Public Health
The Public Health Information and Data Tutorial from the Public Health Partners is an excellent overview of the relationship between Evidence Based Medicine and Evidence Based Pubic Health, and the importance of the topic.
Evidence Based Policymaking (EBP)
(From UK Overseas Development Institutue: Evidence Based Policymaking: Lessons from the UK for developing countries)
"The idea of using evidence to inform policy is not a new idea......
Why does it matter for developing countries?
This matters even more for developing countries. Better utilization of evidence in policy and practice can help save lives, reduce poverty and improve development performance. For example, the Government of Tanzania has used the results of household disease surveys to inform health service reforms that helped reduce infant mortality by 40 per cent. However, the HIV/AIDS crisis has deepened in some countries because governments have ignored the evidence of what causes the disease and how to prevent it spreading. In developing countries, the challenges of evidence-based policy are significantly greater that in the North. Social and political environments are more difficult. Capacity is much more limited and resources are scarcer."
Evidence based Public Health - presentation from the Epidemiology Supercourse. This presentation, one of those from the vast array available from the Epidemiology Supercourse, contrasts the evidence requirements of clinical and Public Health practice, and gives some examples relating to cesarean section.
The population approach.
As you will see in other parts of this module, and more clearly in other modules from the Peoples-uni, there is a real science in the study and application of evidence to populations. Here, we just give a flavour.
Measuring the burden of illness on the population
There are a number of ways of measuring the impact of illness on a population, and the Global Burden of Disease measure as described on the WHO web site gives details of one important method.
Population based interventions are well described by the Public Health Agency of Canada on their web site. This is from part of it:
"Prevention of health problems (e.g., disease, injury) occurs at three levels:
Primary prevention involves activities aimed at reducing factors leading to health problems.
Secondary prevention activities involve early detection of and intervention in the potential development or occurrence of a health problem.
Tertiary prevention is focused on treatment of a health problem to lessen its effects and to prevent further deterioration and recurrence.
Because injury, chronic illness, infectious diseases, acute trauma and other health problems can significantly impact the population, population based prevention strategies are warranted. Prevention activities occur primarily in the health care, public health and primary care systems.
Since the factors leading to health problems are complex and include for example behavioural, socio-economic, cultural and other influences, the population health approach provides a framework for developing prevention strategies where all the determinants of health and their interactions are considered."
Public health interventions are defined by Rychetnik and Frommer as "organised activities intended to promote or protect health or prevent ill health in communities or populations, and are often directed at determinants of health (or ill health). They are distinguished from clinical interventions, which are intended to prevent or treat ill health in individuals. Public health interventions may include the following (singly or in combinations):
government policy at local, state or national level
legislation and regulation
organisational development (including organisational policy)
education (which could have a variety of intended outcomes from behaviour change in communities to professional skill development)
engineering and technical developments (such as clean-water supply systems)
service development and delivery
communication (including social marketing)."
The population approach to prevention is well described in the World Health Report for 2002. http://www.who.int/whr/2002/chapter5/en/index2.html
Another part of the World Health Report summarises the population approach nicely - partly reproduced below:
Population-wide strategies for prevention: from the World Health Report
"It makes little sense to expect individuals to behave differently from their peers; it is more appropriate to seek a general change in behavioural norms and in the circumstances which facilitate their adoption." -- Geoffrey Rose, 1992.
The distribution and determinants of risks in a population have major implications for strategies of prevention. Geoffrey Rose observed, like others before and since, that for the vast majority of diseases "nature presents us with a process or continuum, not a dichotomy". Risk typically increases across the spectrum of a risk factor. Use of dichotomous labels such as "hypertensive" and "normotensive" are therefore not a description of the natural order, but rather an operational convenience. Following this line of thought, it becomes obvious that the "deviant minority" (e.g. hypertensives) who are considered to be at high risk are only part of a risk continuum, rather than a distinct group. This leads to one of the most fundamental axioms in preventive medicine: "a large number of people exposed to a small risk may generate many more cases than a small number exposed to high risk". Rose pointed out that wherever this axiom applies, a preventive strategy focusing on high-risk individuals will deal only with the margin of the problem and will not have any impact on the large proportion of disease occurring in the large proportion of people who are at moderate risk. For example, people with slightly raised blood pressure suffer more cardiovascular events than the hypertensive minority. While a high-risk approach may appear more appropriate to the individuals and their physicians, it can only have a limited effect at a population level. It does not alter the underlying causes of illness, relies on having adequate power to predict future disease, and requires continued and expensive screening for new high-risk individuals.
In contrast, population-based strategies that seek to shift the whole distribution of risk factors have the potential to control population incidence. Such strategies aim to make healthy behaviours and reduced exposures into social norms and thus lower the risk in the entire population. The potential gains are extensive, but the challenges are great as well -- a preventive measure that brings large benefits to the community appears to offer little to each participating individual. This may adversely affect motivation of the population at large (known as the "prevention paradox").