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Why is epidemiology useful?

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Epidemiology offers powerful tools to quantify the degree to which risk factors and humanitarian interventions affect population health in a crisis. These tools include surveys, surveillance, analysis of programme data, and rapid assessment. Often different tools can provide information about the same health outcome or indicator of interest; however, the types of information provided by different tools may differ. As a result, a strategic choice about which tool to use is often required.

In crises, epidemiology (and allied disciplines such as social science and demography) can achieve the following tasks:

  • Benchmarking the severity of a crisis and monitoring its evolution over time. Mortality is the main indicator of the severity of crises, since it is the ultimate outcome of increased exposure, susceptibility, disease progression and case-fatality. Mortality can be measured either prospectively (see pages on Mortality surveillance and Surveillance - Prospective death reporting) or retrospectively (see pages on Surveys - Retrospective data collection).
  • Measuring the degree to which different risk factors are present in the crisis-affected community, and the degree to which populations benefit from interventions to minimise these risk factors. The proportion of displaced people in a newly created camp without access to adequate sanitation facilities (i.e. exposed to the risk factor), and the proportion with such access (i.e. protected by the intervention), are two faces of the same coin. By measuring the latter, we also get insight into the former. Depending on the risk factor in question, epidemiologists will measure either the risk factor itself (e.g. overcrowding) or the coverage of the intervention (e.g. water and sanitation, vaccination, or health services).
  • Monitoring trends in the occurrence of specific diseases over time and identifying emergent threats in a timely fashion (see Morbidity surveillance).

All these measurements are made to provide information to decide what interventions are needed and to carry out programme planning, revision, and evaluation.

Epidemiology is thus a potentially critical component of relief operations. It is essential to policy-makers at all levels, including headquarters and field offices. It is used to inform and evaluate decisions taken at both the macro level (e.g. aid allocation, as in the UN Consolidated Appeals Process) and the micro level (e.g. public health interventions in a given community).

An additional role played by epidemiology is that of advocacy and documentation. Epidemiological studies can illuminate the degree of suffering experienced by crisis-affected populations and shed light on the extent of intentional injury and violations of international humanitarian law, as in Iraq. (Click here for a review of studies of mortality in Iraq since the 2003 invasion). While advocacy and documentation has in the past mostly revolved around deaths directly due to war, there is an increasing awareness of the need to also measure indirect excess mortality, as done recently in the Democratic Republic of Congo (click here to see this report), Darfur (click here to see this report), and northern Uganda (click here to see this report).