Download - Association to Causation
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Association to CausationBY
DR MUHAMMAD TAUSEEF JAVEDCONSULTANT MINISTRY OF
HEALTH MAKKAH&
IPH LAHORE
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Sequence of Studies
Clinical observations
Available data
Case-control studies
Cohort studies
Randomized trials
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Types of Associations
• Real• Spurious
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DEFINITIONS• Observational study• Causation• Etiology• Association• Necessary• Sufficient
Your Assignment: Define these terms
as they apply to epidemiology.
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Koch and Causation• Postulates• Why study association?• Web of causation• Do we need a better way?
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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
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Factors in Causation of Disease
• Predisposing• Enabling• Precipitating• Reinforcing
Your Assignment: Define these terms
as they apply to epidemiology.
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Web of Causation
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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
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Association• Deals with ……………….• Is concerned with ……….• Is the degree of ………….• Has to be scientifically proven …..
Your Assignment: fill in the blanks
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Degrees of Association• No association Direct association
No possibility for associationPossibly associatedAssociatedDirect cause and effect
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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
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Deriving Causal Inferences
• Arriving at causation from association For example, showing that Helicobacter
pylori is directly linked to peptic ulcers
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Perspectives• Causation may be limited• Subject to modification• Perhaps more complex than realized• Sometimes not measureable• “Criteria” are really guidelines
may be subjective