Lecture 14- Association, Causal Inference And Causality

Question 1

What are associations?

Answer 1

Relationships between an exposure and an outcome

Question 2

What are the 3 types of associations?

Answer 2

> artifactual (a.k.a.) relationships
non-causal relationships
causal associations

Question 3

What are artifactual associations?

Answer 3

Associations that can can arise from bias and/or confounding (remember false relationships)

Question 4

Name the 2 different ways in which non-causal associations can occur

Answer 4

> the disease may cause the exposure (rather than the exposure causing the disease)

> the disease and the exposure are associated with a 3rd factor (confounding)
» examples
»» coffee drinking and CHD
»» Down’s syndrome and birth order

Question 5

What are causal associations?

Answer 5

Associations in which the exposure leads tothe outcome (disease)

Question 6

What are the 3 types of causal associations (relationships)?

Answer 6

> sufficient cause
necessary cause
component cause (risk factor)

Question 7

Define/summarize this type of causal association: Sufficient cause

Answer 7

> a set of minimal conditions/events that inevitably produce disease
a cause which precedes a disease, and if present, the disease will occur ( not present = no disease)
» quite rare; apart from genetic abnormalities
» sufficient causes can still have multiple required “components” (termed component causes/risk factors) that collectively act to induce disease

Question 8

Define/summarize this type of causal association: Necessary cause.

Answer 8

> a cause which precedes a diseases and has the following relationship with it:
» cause must be present for the disease to occur, yet the cause may also be present without the disease occurring (must be present for disease to occur but does not guarantee the disease will occur)

Question 9

Define/summarize this type of causal association: Component cause (risk factor)

Answer 9

> something that, if present/active, increases the probability (or likelihood) of a particular disease
» high LDL levels are RFs for AMI
» smoking is a RF for lung cancer

> some patients must be “primed” or susceptible to disease before component causes induce disease (multi-factorial)

Question 10

Name the 2 interactions in causal research.

Answer 10

> synergism (factors work together: both)

> Parallelism (factor work in parallel; either/or)

Question 11

Summarize a synergistic interaction.

Answer 11

The biological-interaction of 2 or more component causes (RFs) such that the combined measure of effect is greater than the sum of the individual effects

> > > (All factors need to be present at the same time in order for the disease to occur—-if only one factor is present the likelihood of disease goes way down)

Question 12

Summarize a parallel interaction.

Answer 12

The biological-interaction of 2 or more component causes such that the measure of effect is greater if either is present

> > > (Either/or type or scenario—- only one factor needs to be present in order for disease to occur)

Question 13

Define: Multiple causation

Answer 13

Multiple component causes working together in concert to collectively become sufficient causes

Question 14

What are the components of Hill’s Criteria/Guidelines?

Answer 14

> strength
> consistency
>>> specificity
> temporality
> biologic gradient
> plausibility
>>> coherence, experiment, analogy

Question 15

Strength, in relation to Hill’s criteria?

Answer 15

> refers to the size of the measure of association (RR/OR/HR)

> the greater the association the more convincing it is that the association might be causal

> a strong association is neither necessary nor sufficient for causality and weakness of an association in neither nor sufficient for absence of causality **

Question 16

Consistency (reproducibility), in relation to Hill’s criteria?

Answer 16

> the repeated observations of an association in different populations under different circumstances in different studies

> consistency may still obscure the truth (remember MHT and the Women’s Health Initiative)**

Question 17

Temporality, in relation to Hill’s Criteria?

Answer 17

> is the necessity that the cause precedes the effect/outcome

> time order also describable
» proximate cause (short-term interval)
» distant cause (long-term interval)

Question 18

Biologic gradient, in relation to Hill’s Criteria?

Answer 18

> presence of a gradient of risk (dose-response) associated with degree of exposure

> remember light vs. heavy smokers

> Caution: some biologic factors demonstrate a threshold effect (i.e., no effect until a certain level of exposure is reached)

Question 19

Plausibility, in relation to Hill’s Criteria?

Answer 19

> presence of a biological feasibility to the association, which can be understood and explained (biologically/physiologically/ medically) (does it make sense?)