Causation in Epidemilogy

1. Before the dawn of the 21st Century and
before the advent of antibiotics , Public
health since aegis
has waged war against
greatest threat to mankind, Plague,
cholera & small pox and has won
convincingly …… .

2. Association ,Causation
Cause and effect in Epidemiology
D R D E O D AT T M S U R YAW A N S H I
(MD COMMUNITY MEDICINE ,KEM,MUMBAI )
A S S I S TA N T P R O F E S S O R
COMMUNITY MEDICINE
DSMCH

3. The work of epidemiology is related to
unanswered questions ,but also
unquestioned answers.

4. Learning Objectives
 What is Association?.
 Types of association.
 Criteria for causation.
 Uses of Epidemiology.

5. Association
 Find the cause of disease
 Hypothesis : two or more variables related /associated
 Proceed to measure the association between the two .

6. Definition of association
 Concurrence of two variables more often than would be





expected by chance.
Association does not always means casual relationship.
Measure by correlation coefficient
+ 1 to – 1
+ 1 positive correlation
- 1 negative correlation

7. Learning Objectives
 Theories of disease causation
 What is cause effect ?
 Criteria for causal association.

8. Theories of causation of disease
 Supernatural theory – Old and medieval period
 Contagion theory (miasma)- Renaissance
 Germ theory (Koch postulates)-Early 19th century
 Epidemiological triad theory
 BEINGS model
 Web of causation
 Epidemiological wheel theory
 The theory of necessary and sufficient cause.

9. Types of association
 Spurious association.
 Indirect association.
 Direct association.

One to one causal

Multi factorial causation

10. Spurious association
Total deliveries
Died
Fatality rate
Home deliveries
1000
25
2.5 %
Hospital deliveries
10,000
400
4%

11. Indirect association
Iodine
deficiency
High
altitude
Endemic
goiter

14. Sea
travel
Reddening
of gums
,bleeding
(Scurvy)

15. Indirect association
Vitamin def
Sea travel
Vitamin C
Reddening
of gums
,bleeding
(Scurvy)

16. Direct
causation
: one to one
causation
Change in one
causes change in
another variable
It is cause one to
one causal
relationship .
Cause effect
relation ship
Factor A must be
present to cause the
outcome B

18. Multi factorial causation
 Multiple factors can
individually cause same
disease of Interest .

19. Multi factorial causation
High fat
diet
 Cumulative effect of
factors causing disease
Lack of
exercise
Uncontrolled
diabetes
CHD

20. Criteria for judging causality
 Temporal association.
 Strength of association.
 Specificity of association.
 Consistency of association
 Biological plausibility
 Coherence of association

21. Criteria of causationTemporality
 The exposure variable
should precede before the
outcome.
 Temporal sequence is
maintained.

22. Strength of association
 How much is the association : measure

Relative risk & Odds ratio

Dose response relationship

Duration response relationship

Cessation relationship.

23. Specificity of association
 80 to 90 % of lung cancers are attributed to smoking

24. Consistency
 Studies conducted by various researchers at various
times have indicated similar cause effect phenomena

25. Biological plausibility
 Is the cause effect phenomena commensurate with
already known facts
 Should stand to reasoning of present day knowledge.

26. Coherence
 Rise in tobacco consumption has led to rise in lung
cancer deaths.
 So when smoking and tobacco consumption was
stopped ,the trend decreased.