Module 4: Causality Flashcards
Cause
An event, condition, or characteristic without which the disease would not have occurred
Characteristics of a cause
- Must precede the effect (proximate vs distant)
- Can be either host or environmental factors (e.g. characteristics, conditions, actions of individuals, events, natural, social, or economic phenomena
- Positive (presence of a causative exposure) or negative (lack of a preventive exposure)
Paradigm
An example that serves as a pattern or model
Historical development of theories of causation
- Divine retribution: imbalance in body “humors” caused by air, water, land, stars, spontaneous generation
- Miasma: Disease caused by miasmas or clouds clinging to the earth’s surface
- Germ Theory of Disease and Henle-Koch Postulates:
- Microorganism must always be present with the
disease - Specificity of a cause; a one-to-one relationship
between an exposure and a disease
- Microorganism must always be present with the
- Web of Causation:
- A paradigm for the causes of chronic diseases
- Multiple causes
- Recent controversies:
- Causation cannot be established
- Causal criteria should be abandoned
K.J. Rothman General Model of Causation (3)
Causal Pies
1. Sufficient cause:
A set of conditions without any one of which the disease would not have occurred (this is one whole pie)
- Component cause:
Any one of the set of conditions that are necessary for the completion of a sufficient cause (this is a piece of the pie) - Necessary cause:
A component cause that is a member of every sufficient cause
Attributes of the Causal Pie (4)
- Completion of a sufficient cause is synonymous with occurrence (although not necessarily diagnosis) of disease
- Component causes can act far apart in time
- A component cause can involve the presence of a causative exposure or the lack of a preventive exposure
- Blocking the action of any component cause prevents the completion of the sufficient cause and therefore prevents the disease by that pathway
Web of Causation (3)
- There is no single cause
- Causes of disease are interacting
- Illustrates the interconnectedness of possible causes
Causal “guidelines” suggested by sir AB Hill (1965) (9)
- Strength of the association
- Consistency
- Specificity
- Temporality
- Biological gradient
- Plausibility
- Coherence
- Experiment
- Analogy
Strength of the association (3)
- The larger the association, the more likely the
exposure is causing the disease - Strong associations are more likely to be causal
because they are unlikely to be due entirely to bias
and confounding - Weak associations may be causal but it is harder to
rule out bias and confounding
Association
A statistical relationship between two or more events, characteristics, or other variables
Association does not equal causation
Consistency
An association is observed repeatedly in different persons, places, times, and circumstances
Specificity
- A single exposure should cause a single disease
- When present, specificity does provide evidence of causality but its absence does not preclude causation
Temporality
The causal factor must precede the disease in time
- ABSOLUTELY ESSENTIAL for causality
Biological Gradient (3)
- A “dose-response” relationship between exposure and disease.
- Persons who have increasingly higher exposure levels have increasingly higher risks of disease
- Some exposures might not have a ‘dose-response’ effect but rather a ‘threshold effect’ below which there are no adverse outcomes
Plausibility/Coherence
Biological or social model exists to explain the association. Association does not conflict with current knowledge of natural history and biology of disease
- Many epidemiological studies have identified cause-effect relationships before biological mechanisms were identified (e.g. the carcinogenic substances in cigarette smoke were discovered after the initial epidemiologic studies linking smoking to cancer)
