4. DEFINITIONS
• Observational study
• Causation
• Etiology
• Association
• Necessary
• Sufficient
Your Assignment:
Define these terms
as they apply to
epidemiology.
5. Koch and Causation
• Postulates
• Why study association?
• Web of causation
• Do we need a better way?
6. 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
7. Factors in Causation of Disease
• Predisposing
• Enabling
• Precipitating
• Reinforcing
Your Assignment:
Define these terms
as they apply to
epidemiology.
9. 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
10. Association
• Deals with ……………….
• Is concerned with ……….
• Is the degree of ………….
• Has to be scientifically proven …..
Your Assignment:
fill in the blanks
11. Degrees of Association
• No association Direct association
No possibility for association
Possibly associated
Associated
Direct cause and effect
12. Guidelines for Judging Whether
An Association Is Causal
• 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
13. Deriving Causal Inferences
• Arriving at causation from association
For example, showing that Helicobacter
pylori is directly linked to peptic ulcers
14. Perspectives
• Causation may be limited
• Subject to modification
• Perhaps more complex than realized
• Sometimes not measureable
• “Criteria” are really guidelines
may be subjective
