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ESA1 - Health & Disease In Populations > Causality Or Association? > Flashcards

Causality Or Association? Flashcards

1
Q

Why is it questionable that any exposures satisfy Koch’s Postulates?

A
  • One exposure can cause several diseases e.g. SMOKING
  • Most diseases are multi-factorial with many contributing causes
  • Disease is usually the result of interaction between host, agent and environment
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2
Q

When is a cause ‘necessary’ and when is it ‘sufficient’?

A
  • Necessary when the cause must ALWAYS precede the disease
  • Sufficient when the cause can initiate the disease ON ITS OWN
  • Causes can be necessary, sufficient, neither or both
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3
Q

Define ‘cause’ in an epidemiological context

A

Cause is an exposure or factor that increases the probability for disease

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4
Q

State Koch’s Postulates (1882)

A
  • Agent must be present in every case of the disease by isolation in pure culture
  • Agent must not be present in cases of any other disease
  • Once isolated, agent must be capable of reproducing the disease in experimental animals and must be recovered from the experimental disease produced
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5
Q

Why is it important to differentiate between causal and non-causal factors?

A
  • Attention to the reduction in risk factors that cause disease will have an effect on population health
  • Attention to non causal factors will waste time, money and effort
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6
Q

Describe the steps of epidemiological reasoning

A
  • Hypothesis
  • Design an analytical study to test the hypothesis
  • Test for validity by excluding association factors such as change, bias and confounding
  • DOES THE STATISTICAL ASSOCIATION SHOW A CAUSE-EFFECT RELATIONSHIP???
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7
Q

What are the key assumptions in Epidemiology?

A
  • That the disease does not occur at random

- That the disease have causal and preventable factors that can be identified through systematic investigation

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8
Q

What is meant by association?

A
  • STATISTICAL DEPENDANCE between two or more events, characteristics or other variables
  • The presence of association DOES NOT always imply a causal relationship
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9
Q

What is meant by reverse causality?

A
  • Cause-Effect relationship exists in the opposite direction
  • Believe X causes Y when in fact Y causes X
  • This is a common problem in CASE CONTROL STUDIES because you cannot be certain that the exposure precedes the outcome
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10
Q

Define information bias

A

Error due to systematic differences in the measurement or classification of subjects in the groups being studied

  • RECALL BIAS
  • PUBLICATION BIAS
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11
Q

Define selection bias

A

Error due to systematic differences in the characteristics of the groups being studied due to differences in the way they were selected

  • HEALTHY WORKER EFFECT
  • ALLOCATION BIAS
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12
Q

What is the effect of reverse causality?

A

May result in true associations which occur other than the proposed causal link

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13
Q

What factors may cause apparent associations to arise?

A
  • Chance
  • Bias
  • Confounding
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14
Q

What is meant by bias?

A

Deviation of the results from the truth due to systematic errors

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15
Q

How could you test for validity of an analytical study?

A
  • Remove the assumption that the results were due to chance using p-value and 95% CI
  • Excluding possible bias and confounding factors
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16
Q

What are the main Bradford Hills criteria for association factors?

A
  • STRENGTH
  • SPECIFICITY
  • CONSISTENCY
17
Q

What is meant by STRENGTH OF ASSOCIATION?

A
  • A STRONG ASSOCIATION IS MORE LIKELY TO BE CAUSAL
  • Strong associations are less likely to be explained by undetected bias or confounding factors
  • However weak associations may still be causal
18
Q

What is meant by SPECIFICITY OF ASSOCIATION?

A
  • ASSOCIATION THAT IS SPECIFIC TO THE EXPOSURE-DISEASE ASSOCIATION UNDER INVESTIGATION IS MORE LIKELY TO BE CAUSAL
  • However most diseases are multifactorial and several exposures can cause several different diseases
19
Q

What is meant by CONSISTENCY OF ASSOCIATION?

A
  • ASSOCIATION THAT HAS BEEN DEMONSTRATED IN MULTIPLE DIFFERENT STUDIES ON DIFFERENT GROUPS OF PEOPLE AT DIFFERENT TIMES IS MORE LIKELY TO BE CAUSAL
  • Unlikely to explained by the same bias or confounding
  • Lack of consistency may be due to differences in study designs or other causal factors
20
Q

What Bradford Hulls criteria are specific to the exposure/outcome relationship?

A
  • Temporal sequence
  • Dose response
  • Reversibilty
21
Q

What is meant by TEMPORAL SEQUENCE?

A
  • ASSOCIATION WHERE THE EXPOSURE IS DEMONSTRATED TO PRECEDE THE OUTCOME IS MORE LIKELY TO BE CAUSAL
  • Strength of this criterion is in its corollary (if the outcome precedes the exposure then the exposure cannot be said to cause the outcome)
22
Q

What is meant by DOSE RESPONSE?

A
  • IF VARYING AMOUNTS OF EXPOSURE LEADS TO VARYING STRENGTHS OF ASSOCIATION WITH THE OUTCOME OF INTEREST THIS IS MORE LIKELY TO BE CAUSAL
  • Unknown confounders and bias are unlikely to be operating to the same degree in the varying associations of the exposure and outcome
23
Q

What is meant by REVERSIBILITY?

A
  • ASSOCIATION IN WHICH REMOVAL OF THE EXPOSURE OR PUTATIVE FACTOR LEADS TO A REDUCED OR NON-EXISTENT RISK OF ACQUIRING OUTCOME IS HIGHLY LIKELY TO BE CAUSAL
  • Strongest criterion for inferring causality but is sometimes difficult to demonstrate
24
Q

What other evidence in Bradford Hills is used for inferring causality?

A
  • Coherence of theory
  • Biological plausibility
  • Analogy
25
Q

What is meant by COHERENCE OF THEORY?

A
  • ASSOCIATION THAT CONFIRMS WITH CURRENT KNOWLEDGE AND THEORY IS MORE LIKELY TO BE CAUSAL
  • However there are examples in biomedical science where causal links have been established with did not conform to contemperous thinking
26
Q

What is meant by BIOLOGICAL PLAUSIBILITY?

A
  • ASSOCIATION FOR WHICH THERE IS A BIOLOGICALLY PLAUSIBLE MECHANISM IS MORE LIKELY TO BE CAUSAL
  • However this is limited by current knowledge of biological mechanisms
  • Presence of a biological mechanism does not guarantee that an association or effect will exist
27
Q

What is meant by ANALOGY?

A
  • ASSOCIATION FOR WHICH AN ANALOGY OR INFERENCE EXISTS IS MORE LIKELY TO BE CAUSAL
  • This is the weakest argument for inferring causality
28
Q

How can results be validated externally?

A

Comparison to reference population and general population

29
Q

How can results be validated internally?

A
  • Assess results for non causal associations by excluding bias, confounding factors, chance and reverse causality
  • Test features of causality to determine whether there is statistical evidence for a cause-effect relationship (STRENGTH, DOSE RESPONSE, SPECIFICITY, REVERSE CAUSALITY)
30
Q

What is an ecological comparison?

A

Exposure and outcome are not linked on an individual basis

ESA1 - Health & Disease In Populations (9 decks)

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