1. Association to Causation
1. Recall the epidemiologic triangle and the epidemiologic wheel as models of disease in the human host. Any can be involved in association and causaation.
2. We might use animals or tissue culture t o examine for causation. However, animals don’t always work because of dosage differences and tissue culture is artificial.
3. Therefore, we need to make observations in people. Can’t use as guinea pigs, so can’t have randomized groups. So we rely on clinical observations, case-control and cohort studies.

2. Clinical observations
Sequence of Studies
Clinical observations
Available data
Case-control studies
Cohort studies
Randomized trials
1. Studies might follow this sequence.
2. Good example is Doll etal. use of available info to case-control study association of cig. Smoking and lung cancer
3. To determine assoc or causation:
a. Use studies of group characteristics:ecologic studies
b. Studies of individual characteristics: case control studies
If an association is found , then determine if it’s causal.

3. Types of Associations Real Spurious
Is the association real or spurious. Recall the presumed association between coffee consumption an pancreatic cancer.
For association, is it real. Important because we then try to find an intrvention or a treatment. If it’s not real, then we have wasted a lot of time and resources. For example, intending to lower cholesterol levels.

4. DEFINITIONS Observational study Causation Etiology Association
Necessary
Sufficient
Your Assignment:
Define these terms
as they apply to
epidemiology.
1. Observational study- one that is based on non-random survey of populations
2.Causation - a factor(s) that is absolutely responsible, completely or in part, for the occurrence of disease.
3. Association - a factor(s) that is related, completely or in part, to the occurrence of disease.
4.Necessary and sufficient - there are four types of causal relationships that may be required - either, both or neither

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.
Predisposing - aleady present
Enabling- essential to development of disease
Precipitating - also, development and continuation of disease
Reinforcing - like enabling but these are repetitive behaviours which support disease condition.

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