ep test 2e
Terms
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- Causality
- A special association in which a potential risk factor leads to a health outcome Related terms: causal factor; causal relationship; etiology;
- Establishing Causality-study designs
- Case reports and series Ecologic studies and surveillance data Cross-sectional studies Case-control studies Cohort studies Intervention studies/randomized trials
- Types of Causal Models
- Necessary and Sufficient uncommon; sole cause of disease, that always causes disease – rabies, ebola Necessary but Not Sufficient much more frequent; multiple factors needed to express disease - TB Sufficient but Not Necessary rare; multiple factors can independently produce disease – smoking and lung cancer Neither Sufficient Nor Necessary common in chronic disease; multiple factors that can combine in several ways to promote disease occurrence, but disease does not always occur – obesity, smoking and CVD
- Koch's Postulates
- Organism must be consistently present in cases of disease Organism suspected of causing disease must be able to be isolated and cultured Cultured organism must initiate disease when experimentally introduced to a new host
- Establishing Causality 1
- Strength of the association Biologic plausibility Temporal association Consistency across multiple studies (reproducibility)
- Establishing Causality 2
- Elimination of “reasonable doubt†and alternative explanations Dose response Cessation of exposure Specificity of the association Consistency with other knowledge
- Causality is a Collective Determination
- Multiple studies in different sites and populations Often over many years Ideally including experimental studies Finally, results in a consensus decision on interpretation of the findings