Causality

Question 1

What is a confounder?

Answer 1

a variable that influences both the dependent variable and independent variable
- is a causal inference

Question 2

Name study designs with the highest causality to the lowest?

Answer 2

1. clinical trial
2. cohorts
3. case-control
4. cross-sectional
5. ecological studies

Question 3

What is a cause?

Answer 3

a cause of a disease in an event, condition, characteristic or a combination of these factors which plays an important role in producing the disease
- cause must preceed the disease
- a cause is termed sufficient when it inevitably produces or initiates a disease and is termed necessary if a disease cannot develop in its absence

Question 4

What are the factors in causation?

Answer 4

1. predisposing factors
2. enabling factors
3. precipitating factors
4. reinforcing factors
   Note: all may be necessary but they are rarely sufficient to cause a particular disease or state

Question 5

What are predisposing factors?

Answer 5

factors that may create a state of susceptibility to a disease agent
e.g. age, sex and previous illness

Question 6

What are precipitating factors?

Answer 6

precipitating factors such as exposure to a specific disease agent or noxious agent may be associated with the onset of a disease or state

Question 7

What are reinforcing factors?

Answer 7

reinforcing factors such as repeated exposure and unduly hard work may aggravate an established disease state

Question 8

What are enabling factors?

Answer 8

factors that may favour the development of disease
e.g. low income, poor nutrition, bad housing and inadequate medical care
Note: circumstances that assist in recovery from illness or in the maintenance of good health could also be enabling factors

Question 9

What is the Bradford Hill criteria?

Answer 9

are a group of nine principles that can be useful in establishing epidemiologic evidence of a causal relationship between a presumed cause and an observed effect and have been widely used in public health research
- They were established in 1965 by the English epidemiologist Sir Austin Bradford Hill

Question 10

Name the 9 guidelines of the Bradford Hill criteria?

Answer 10

1. temporal sequence of association
2. strength of the association
3. consistency of association
4. biological gradient (dose response)
5. specificity of association
6. plausibility of association
7. coherence of association
8. experiment (reversibility)
9. analogy

Question 11

What is temporal sequence of association?

Answer 11

the exposure must precede outcome
- to exclude reverse causation

Question 12

Name the optimal study designs used to study temporal sequence of association?

Answer 12

1. RCT
2. prospective cohort

Question 13

Name weak study designs that can not study temporal sequence of association?

Answer 13

1. cross sectional
2. case control

Question 14

What is strength of association?

Answer 14

the stronger the association or magnitude of the risk between a risk factor and outcome, the more likely the relationship is thought to be causal

Question 15

How do you measure strength of association?

Answer 15

measure of effect
1. Rate Ratio
2. Risk Ratio
3. OR
- strong associations less likely to be due to undetected confounding
- weak associations may be causal

Question 16

What is consistency of association?

Answer 16

the same findings have been observed among different populations using different study designs and at different times
- association shown in many different study designs & populations
- less likely to have same bias and confounding

Question 17

What is biological gradient?

Answer 17

changes in the intensity of the exposure results in a change in the severity or risk of the outcome
- increase risk of outcome with increase increased exposure
- lack of dose response does not mean no causality : threshold effect

Question 18

What is specificity of association?

Answer 18

there is a one to one relationship between exposure and outcome
- occurs when single factor associated with single outcome
- becoming less relevant e.g. smoking

Question 19

What is plausibilty of association?

Answer 19

there is a potential biological mechanism which explains the association
- acceptance depends on how likely association is
- reported association may stimulate research into association

Question 20

What is coherence of association?

Answer 20

the relationship found agrees with the current knowledge of the natural history/biology of the disease
- reported association does not conflict with current knowledge
- can lead to publication bias, can discourage search for alternative hypothesis

Question 21

What is experiment (reversibility)?

Answer 21

removal of the exposure alters the frequency of the outcome
- removal of exposure leads to reduction in risk

Question 22

What is analogy?

Answer 22

the relationship is in line with other established cause-effect relationships
- other similar demonstrated associations
e.g. knowing the teratogenic effects of thalidomide we may accept a cause effect relationship for a similar agent based on slighter evidence