To gain full benefit from this resource it is important to have an understanding of epidemiologic concepts, notably causal associations , and to be aware of issues which may influence apparent association, notably bias, confounding, and chance. To enable an understanding of the role and application of occupational epidemiology. Drawing analogies between the clinical and epidemiologic approach. The above analogies can be extended to the history taking process. The term is now applied epidemiologically to a clearly defined population who prospectively share a common experience -say an occupational exposure.
Some cohort studies measure mortality, others measure incidence of disease.
The incidence rate is defined as the number of NEW cases of a disease divided by the population at risk over a given period of time. In occupational and environmental epidemiology it is important to be able to characterise the exposure of the 'population at risk'. For example a study was conducted in which workers were followed up during their employment in a factorybin which they were exposed to benzene. It showed that those categories of workers with a high cumulative exposure to benzene had a higher mortality from certain types of leukaemia than the control population. The Healthy Worker Effect Workers differ from the general population from which they are drawn, and especially from unemployed people in many ways.