Lecture 21: Causality

Question 1

What is the definition of the public/population health model?

Answer 1

“To provide the maximum benefit for the largest number of people- at the same time reducing inequities in the distribution of health and wellbeing”

Question 2

What is individual healthcare concerned with?

Answer 2

The treatment or restoration of health for the individual by a clinician (so it is reactive)

Question 3

What is population health concerned with?

Answer 3

The health of groups of individuals, in the context of their environment (a comprehensive, proactive population approach to clinical practice)

Question 4

Does epidemiology determine the cause of disease in an individual?

Answer 4

No

Question 5

What does epidemiology determine?

Answer 5

The relationship or association between a given exposure and disease in a population

Question 6

Can preventative action be taken before the cause is identified? What is an example?

Answer 6

Yes, for example, James Lind’s treatment of scurvy (1747)

Question 7

What are two frameworks to determine causality?

Answer 7

1. Bradford Hill Criteria “aids to thought” 1965

2. Rothman’s Causal Pies

Question 8

What are the seven components of Bradford Hill’s Criteria?

Answer 8

1. Temporality
2. Strength of Association
3. Consistency of Association
4. Biological Gradient (dose-response)
5. Biological Plausibility of Association
6. Specifity of Association
7. Reversibility
   JUDGEMENT

Question 9

What is the weakest component of Bradford Hill’s criteria?

Answer 9

6. Specifity of association, because a single cause often leads to multiple effects

Question 10

Define temporality

Answer 10

The cause comes before the disease (essential to establish a causal relation)

Eg smoking comes before lung cancer deaths

Question 11

Define strength of association

Answer 11

The stronger the association, the more likely to be causal in the absence of known bias (selection, information and confounding)

Eg smoking/lung cancer risk ratio >10

Question 12

Define consistency of association

Answer 12

Replication of the fi dings by different investigations, at different times, in different places, with different methods

Eg multiple studies showed similar results

Question 13

Define biological gradient (dose exposure)

Answer 13

Incremental change in disease rates in conjunction with corresponding changes in exposure

Eg increased smoking per day showed higher risk of lung cancer

Question 14

Define biological plausibility of association

Answer 14

Does the association make sense biologically?

Eg chemicals in tobacco (carcinogens) are known to promote cancer

Question 15

Define specificity of association

Answer 15

A single cause leads to a single effect (often a single cause has multiple effects, however)

Eg smoking has multiple outcomes

Question 16

7. Define reversibility

Answer 16

The demonstration they under controlled conditions, changing the exposure causes a change in outcome

Eg reduced risk in lung cancer after quitting smoking

Question 17

Does causal phenomena usually equal 1:1?

Answer 17

No, causal phenomena is usually complex and exposure-outcome relationships are not usually 1:1

Question 18

What is the definition of a cause of disease?

Answer 18

An event, condition, characteristic (or combination of these factors) which play an essential role in producing the disease

Question 19

What is the “sufficient” cause of a causal pie?

Answer 19

Is a factor/s that will inevitably produce the specific disease (ie causal mechanism or 1 pie)

Question 20

What is a “component” cause of a causal pie?

Answer 20

A factor that contributes towards a disease causation but is not sufficient to cause a disease on its own

Eg poor sanitation in regards to TB disease (a slice of pie that’s not necessary)

Question 21

What is a “necessary” cause of a causal pie?

Answer 21

A factor (or component cause) that must be present for a specific cause to occur

Eg the TB bug

Question 22

Can you intervene at any number of points in the pie?

Answer 22

YES
Knowledge of the complete pathway is not w prerequisite for introducing preventative measures

Ie TB prevention occurred before its cause was discovered

Question 23

What do we use association and several other factors for?

Answer 23

To infer causation and to intervene to prevent disease

Question 24

Is a necessary cause still a component cause?

Answer 24

Yes, because it’s still part of the pie

Question 25

What do epidemiologists look for links between?

Answer 25

Exposure and outcome