Question

Describe in your own works Criteria of Causation and how it relates to exposure and a suspected risk factor?

Answer 1

Criteria of causation helps to identify the relationship between a presumed cause and its effect by observation. This provides evidences for epidemiological studies. The cause of a disease depends on multiple factors. In research activities pertaining to public health the emphasis is on identifying relevant causes on which interventions can be developed in order to prevent the progress of a disease. Majority of such researches are non experimental and the results thus lack base of strong evidences to support the findings. Causation is thus a logical inference drawn after a series of observations regarding the conjunction between two factors (exposure and health status) . There are nine set of criteria that can provide epidemiological evidence on causational relationship suggested by Bradford Hill, an English statistician in 1965. Those criteria includes :

Strength - though a larger association between the suspected risk factor(cause) and its effect(disease) indicates a higher chances of causational relationship, a smaller association cannot be ignored or nullified.

Consistency - Results of the same study conducted by different individuals in different settings on different population measures the reproducibility of the results and suggests strong causational relationship.

Specificity - as the specificity increases in relation to the increased association between a suspected cause and its effect. The chances of a more probable causational relationship is also high in such cases.

Temporality - the expected time between the cause and effect should be correct. That is some diseases occurs immediately after exposure where as some pathogens goes through an incubation period before onset of symptoms

Biological gradient - Basically exposure in large amount leads to increased incidences. But there is chances of inverse relationship too. That is even a small amount of exposure can cause higher incidences or higher amount of exposure may not lead to expected higher rates of incidences. This is based on individual factors.

Plausibility - a reasonable mechanism of interaction between the cause(risk factor) and effect (disease) may be helpful in establishing the causational relationship. For example a proper explanation of pathophysiology helps to understand the probable causes and each of its effect on the human body.

Coherence - consistency of findings both from epidemiological perspective and laboratory values may strengthen the findings. But inconsistency between the two does not totally rule out chances of relationship between cause and effect

Experiment - experimental evidences provides evidence based data. But the access to such experimental findings are limited as it is unethical to expose a group of people to a potential risk factor to evaluate the results that are unknown and may possibly have severe consequences.

Analogy - comparison of findings of different observations may help to identify similarities.