Transcript Association to Causation Sequence of Studies Clinical observations Available data Case-control studies Cohort studies Randomized trials.

Association to Causation
Sequence of Studies
Clinical observations
Available data
Case-control studies
Cohort studies
Randomized trials
Types of Associations
• Real
• Spurious
DEFINITIONS
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Observational study
Causation
Etiology
Your Assignment:
Define these terms
Association
as they apply to
epidemiology.
Necessary
Sufficient
Koch and Causation
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Postulates
Why study association?
Web of causation
Do we need a better way?
Twelve Criteria for Causation
• Cause distributed at
same level
• Incidence much
higher in exposed
population
• Exposure more
frequent
• Disease should
follow exposure
• Dose dependent
• Expected response
• Association should be
the same
• Other cause-effect ruled
out
• Control results in
decreased disease
• Modification of host
results in decrease
• Human vol. always +
• Findings should make
sense
Factors in Causation of Disease
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Predisposing
Enabling
Precipitating
Reinforcing
Your Assignment:
Define these terms
as they apply to
epidemiology.
Web of Causation
Are Associations Always
Connected to the Disease?
NO, BUT …………………………..
Cigarette smoking and lung cancer
Age and prostate cancer
Car accidents and alcohol
Tribal customs and kuru
Agriculture and antibiotic resistance
Association
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Deals with ……………….
Is concerned with ……….
Is the degree of ………….
Has to be scientifically proven …..
Your Assignment:
fill in the blanks
Degrees of Association
• No association
Direct association
No possibility for association
Possibly associated
Associated
Direct cause and effect
Guidelines for Judging Whether
An Association Is Causal
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Temporal relationship
Strength of the association
Dose-response relationship
Replication of the findings
Biologic plausibility
Consideration of alternate explanations
Specificity of the association
Consistency with other knowledge
Deriving Causal Inferences
• Arriving at causation from association
 For example, showing that Helicobacter
pylori is directly linked to peptic ulcers
Perspectives
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Causation may be limited
Subject to modification
Perhaps more complex than realized
Sometimes not measureable
“Criteria” are really guidelines
may be subjective