8. Causality: Cause or Merely Association?

Question 1

What is a cause?

Answer 1

An exposure or factor that increases the probability of disease.

Question 2

What is the purpose of working out the cause of a disease etc?

Answer 2

To use the knowledge gained to remove, avoid or protect against harmful factors.

Question 3

What do cohort studies and case control studies investigate have in terms of proving a causal link?

Answer 3

Cohort studies study if there is an association between exposure and developing the outcome.
Case control studies study if there is an association between being a case and have had the exposure.

Question 4

What are some possible explanations for systematic and random variation?

Answer 4

Confounding - known, possible or Unknown factors.
Bias - selection or information.
Chance - measured by p-value and confidence interval.

Question 5

How can the strength of evidence for a cause-effect relationship be evaluated?

Answer 5

Using Bradford Hill’s viewpoints or criteria for inferring causality.

Question 6

What are the association features evaluated in Bradford Hill’s viewpoint?

Answer 6

Strength, specificity and consistency of association.

Question 7

What are the exposure/ outcome features evaluated in Bradford Hill’s viewpoint?

Answer 7

Temporal sequence, dose response and reversibility.

Question 8

What are other evidence is evaluated in Bradford Hill’s viewpoint?

Answer 8

Coherence of theory, biological plausibility and analogy.

Question 9

What does the Bradford Hill’s criteria suggest about the impact strength of association has on how likely a cause-effect relationship is?

Answer 9

A causal link is more likely with strong associations.

Question 10

What does the Bradford Hill’s criteria suggest about the impact specificity of association has on how likely a cause-effect relationship is?

Answer 10

Causal link more likely when an outcome is associated only with a specific factor.

Question 11

What does the Bradford Hill’s criteria suggest about the impact consistency of association has on how likely a cause-effect relationship is?

Answer 11

A causal link is more likely if the association is observed in different studies and different sub-groups.

Question 12

What does the Bradford Hill’s criteria suggest about the impact temporal sequence has on how likely a cause-effect relationship is?

Answer 12

A causal link is more likely if exposure to the putative factor has been shown to precede the outcome.

Question 13

What does the Bradford Hill’s criteria suggest about the impact dose response has on how likely a cause-effect relationship is?

Answer 13

A causal link is more likely if different levels of exposure to the putative factor leads to different risk of acquiring the outcome.

Question 14

What does the Bradford Hill’s criteria suggest about the impact reversibility has on how likely a cause-effect relationship is?

Answer 14

A causal link is very likely if removal or prevention of the putative factor leads to reduced or non-existent risk of acquiring the outcome.

Question 15

What does the Bradford Hill’s criteria suggest about the impact coherence of theory has on how likely a cause-effect relationship is?

Answer 15

A causal link is more likely if the observed association conforms with current knowledge.

Question 16

What does the Bradford Hill’s criteria suggest about the impact biological plausibility has on how likely a cause-effect relationship is?

Answer 16

A causal link is more likely if a biologically plausible mechanism is likely or demonstrated.

Question 17

What does the Bradford Hill’s criteria suggest about the impact analogy has on how likely a cause-effect relationship is?

Answer 17

A causal link is more likely if an analogy exists with other diseases.

Question 18

What is epidemiology?

Answer 18

The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to the control of health problems.

Question 19

What two assumptions are made in epidemiology?

Answer 19

Disease does not occur at random, disease has causal and preventable factors that can be identified through systematic investigation.

Question 20

What are the three requirements of Henle-Koch’s Postulates germ theory?

Answer 20

The agent must be necessary (in every case), specific (not found in other diseases) and sufficient (capable of reproducing the disease in experimental animals).