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Association to CausationBY
DR MUHAMMAD TAUSEEF JAVEDCONSULTANT MINISTRY OF
HEALTH MAKKAH&
IPH LAHORE
Sequence of Studies
Clinical observations
Available data
Case-control studies
Cohort studies
Randomized trials
Types of Associations
• Real• Spurious
DEFINITIONS• Observational study• Causation• Etiology• Association• Necessary• Sufficient
Your Assignment: Define these terms
as they apply to epidemiology.
Koch and Causation• 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
• 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 cancerAge and prostate cancerCar accidents and alcoholTribal customs and kuruAgriculture and antibiotic resistance
Association• 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 associationPossibly associatedAssociatedDirect cause and effect
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
Deriving Causal Inferences
• Arriving at causation from association For example, showing that Helicobacter
pylori is directly linked to peptic ulcers
Perspectives• Causation may be limited• Subject to modification• Perhaps more complex than realized• Sometimes not measureable• “Criteria” are really guidelines
may be subjective