1. Association to Causation
BY
DR MUHAMMAD TAUSEEF JAVED
CONSULTANT MINISTRY OF
HEALTH MAKKAH
&
IPH LAHORE

2. Sequence of Studies
Clinical observations
Available data
Case-control studies
Cohort studies
Randomized trials

3. Types of Associations
• Real
• Spurious

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.

8. Web of Causation

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