Causation and Association

Modified guidelines for Evaluating the Causal relationship (in order of priority)

*Major Criteria* - Temporal Relationship - Biological Plausibility - Consistency *Others:* - Dose-Response Relationship - Strength of association - Cessation effects

Temporality

- Exposure to causative factor must occur before disease develops and should allow for any latent period - Absolutely necessary for causality

Consistency of Association

- Finding is similar in different places in different populations with different study methods

Dose-Response Related

- Increasing causative factor = increasing amounts of disease - Some cases have a threshold, (disease does not develop until a certain level has reached)

Strength of association

- Ratio is calculated for disease rates for those with and without the causative factor - Greater the ratio, the more likely it is to be a causal relationship - Weaker associations are more likely to be explained by undetected bias (but does not rule out causation)

Bradford Hill's Criteria

- Strength of Association - Dose-Reponse Related - Consistency of association - Temporality - Specificity of association - Biological plausibility - Reversibility

When studies find an association between 2 things:

...it does not mean one thing caused the other to happen

Biological plausibility

A biological mechanism should explain why this occurs. Association must be consistent with other knowledge (mechanism of action, etc.)

Specificity

Every time the causative factor occurs, there will be a case Closer the one-on-one relationship, the greater the specificity Less important than the previous criteria

Reversibility

Removing the causative factor should produce less cases of the disease