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CIC SURVEILLANCE AND EPIDEMIOLOGIC INVESTIGATION

Terms in this set (50)

D The onset of disease must precede exposure to the causal factor

Rationale: The criteria for causality are known as Hill's criteria and use epidemiological methods to determine whether a factor is causal for a given disease. Hill's criteria for causation are as follows:

1. Strength of association: The incidence of disease should be higher in those who are exposed to the factor under consideration than in those who are not exposed; that is, the stronger the association between an exposure and a disease, the more likely the exposure is to be causal. For example, lung cancer is common in those who smoke.
2. Consistency: This means that the association should be observed in numerous studies, preferably by different researchers using different research methodologies.
3. Specificity Refers to an association between one factor and one disease, and this association is more likely to be causal. This criterion also refers to the extent to which the occurrence of one factor can be used to predict the occurrence of another (disease). In reality, such a one-to-one relationship is rare due to the multifactorial causes of most diseases and because, sometimes, the same factor(s) can cause more than one disease.
4. Temporality: This must also be addressed when determining cause of disease. Essentially, exposure to the hypothesized causal factor must precede the onset of disease.
5. Biological gradient: The biological gradient is a dose-response relationship between increased exposure to a factor and increased likelihood of disease. For example, the longer one smokes, the more likely one is to develop lung cancer. If the association demonstrates a biological gradient between the factor (exposure) and effect (disease), the relationship is more likely to be causal.
6. Plausibility: The association in question should also be biologically plausible in light of current knowledge. This criterion may be the most elusive and variable of the nine. Because biological knowledge is ever expanding, lack of biological plausibility does not necessarily disprove a theoretical association.
7. Coherence: There should be coherence between known information about the biological spectrum of the disease and the associated factor, that is, the association should be in accordance with other facts known about the natural history of the disease.
8. Analogy: Associations derived from experiments add considerable weight to evidence supporting causal associations. These experiments can be animal model studies or clinical trials; however, although animal models may be helpful, many diseases do not manifest the same way in animals and humans.
9. Finally, if similar associations have been shown to be causal, by analogy the association is more likely to be causal. Determining causality may also help to determine at which points the natural history of a disease may be interrupted, so that prevention and control efforts are effective. It can also add information on the natural history of a disease.