病例定义(施国庆201103北京).pptVIP

* More than 50 years ago Bradford Hill laid out 9 criteria for causation in epidemiology. Since then others have suggested minor additions or modifications to these findings but on the whole they still serve us well in in judging the quality of epidemiologic findings. Among the 9 criteria 3 apply more directly to analytic (case control and cohort studies) Strength of the association, Specificity of the association, Dose reponse effect. Bradford hill wrote these with a specific practical purpose – to help epidemiologists decide at what point they had sufficient evidence to take preventive action.” Today I will discuss the utility of the dose response effect both in terms of the degree of exposure and the severity of the disease. “)???? Biological gradient: Fifthly, if the association is one which can reveal a biological gradient, or dose-response curve, then we should look most carefully for such evidence. For instance, the fact that the death rate from cancer of the lung rises linearly with the number of cigarettes smoked daily, adds a very great deal to the simpler evidence that cigarette smokers have a higher death rate than non-smokers. The comparison would be weakened, though not necessarily destroyed, if it depended upon, say, a much heavier death rate in light smokers and a lower rate in heavier smokers. We should then need to envisage some much more complex relationship to satisfy the cause and effect hypothesis. The clear dose-response curve admits of a simple explanation and obviously puts the case in a clearer light. ? The same would clearly be true of an alleged dust hazard in industry. The dustier the environment the greater the incidence of disease we would expect to see. Often the difficulty is to secure some satisfactory quantitative measures of the environment which will permit us to explore this dose-response. But we should invariably seek it. * * For many diseases both infectious and non-infectious the severity of disease