lecture 11 Flashcards
What is the cause of the problem?
An important role of epidemiology is to seek the cause of “dis-ease”
Establishing causal relationships is important to provide support for evidence-based practice
What is the cause of the problem?
Epidemiology does not determine the cause of a disease in an individual
Sometimes, preventive measures can be
put in place before we determine the
cause of a disease
Causality
Causality cannot be proved in human experimental studies (for practical and ethical reasons)
Most epidemiological studies,
o are non-experimental
o are conducted in ’noisy’ environments in
free-living populations
o determine the relationship or association
between a given exposure to a cause/s and
dis-ease outcome in populations
Epidemiology can identify
Epidemiology can identify a statistical association between a potential ‘exposure’ and an ‘outcome’
Does this mean the exposure causes the outcome?
Sometimes, but not always
Establishing causal
Establishing causal inference should be done cautiously
When looking for links between Exposure &
Outcome:
Need sufficient studies done in diverse settings and adequately limiting random errors, non- random errors (bias) and confounding
Judge findings against a framework to see if
the association is causal
British Doctors Study
Doll & Hill (1951-1961)
* Death rates from lung cancer associated with
cigarette smoking
radford Hill Framework (1965)
Criteria (aspects/features)
1. Temporality
2. Strength of association
3. Reversibility
4. Biological gradient (dose-response)
5. Biological plausibility of association
6. Consistency of association
7. Specificity of association
Temporality
- First the cause then the disease
- Essential to establish a causal relation
Strength of association
The stronger an association, the more likely to be causal in absence of known biases (selection, information, and confounding
Reversibility
The demonstration that under controlled conditions, a change
in exposure results in a change in the outcome
Biological gradient (dose-response)
- Incremental change in disease rates in conjunction
with corresponding changes in exposure
Biological plausibility of association
Does the association make sense biologically?
Chemicals in tobacco that are known to promote cancers
(carcinogens)
Consistency of association
Replication of the findings by different investigators, at different
times, in different places, with different methods
Multiple studies have shown similar results
Specificity of association
A cause leads to a single effect
Many diseases share causes
Smoking → Lung cancer, CVD, other respiratory disease etc.
An effect has a single cause
Diseases have multiple causes
Lung cancer is caused by smoking, exposure to asbestos etc.
The Epidemiological Triad
A cause of a disease
an event, condition, characteristic (or combination of these factors) which play an essential role in producing the disease
Causal pie
Recognises multicausality
Sufficient cause
Component cause
Necessary cause
Tuberculosis (TB)
A causal pie for TB
