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Association to Causation. Clinical observations. Available data. Case-control studies. Cohort studies. Randomized trials. Sequence of Studies. Types of Associations. Real Spurious. DEFINITIONS. Observational study Causation Etiology Association Necessary Sufficient.

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sequence of studies

Clinical observations

Available data

Case-control studies

Cohort studies

Randomized trials

Sequence of Studies
  • Observational study
  • Causation
  • Etiology
  • Association
  • Necessary
  • Sufficient

Your Assignment:

Define these terms

as they apply to


koch and causation
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

Twelve Criteria for Causation
factors in causation of disease
Factors in Causation of Disease
  • Predisposing
  • Enabling
  • Precipitating
  • Reinforcing

Your Assignment:

Define these terms

as they apply to


are associations always connected to the disease
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
  • Deals with ……………….
  • Is concerned with ……….
  • Is the degree of ………….
  • Has to be scientifically proven …..

Your Assignment:

fill in the blanks

degrees of association
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
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
Deriving Causal Inferences
  • Arriving at causation from association
    • For example, showing that Helicobacter pylori is directly linked to peptic ulcers
  • Causation may be limited
  • Subject to modification
  • Perhaps more complex than realized
  • Sometimes not measureable
  • “Criteria” are really guidelines
    • may be subjective