II MBBS class - epidemiology series

1. Association & Causation
‘omne ignotum pro magnifico’
Dr. Rizwan S A, M.D.,
Assistant Professor,
Department of Community Medicine,
VMCH&RI, Madurai.
03.11.2014
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2. Classification of research methods
Research
methods
Observational
Descriptive
Case series,
case reports,
CS, cohort
Analytical
Ecological Cross-
sectional
Cohort Case control
Experimental
Controlled Uncontrolled
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3. Procedures in descriptive epidemiology
1. Define the population
2. Define and describe the disease
3. Measure the disease
4. Compare
5. Formulate hypothesis
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4. Examples
S.No. Cause Effect
1 Mycobacterium tuberculosis
2 Measles virus
3 Obesity
4 Hypercholesterolemia
5 Excess salt intake
6 Crime
7 Domestic violence
8 Cholera outbreak
9 Polio
10 Congenital anomaly
11 COPD
12 Cancer
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5. Association
• Terms - association and relationship used
interchangeably
• Defined as the co-occurrence of two or more
variables at a frequency which is more than
that expected by chance
• Association does not mean causation
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6. Types of association
1. Spurious association
2. Indirect association
3. Direct (causal) association
I. One to one causal association
II. Multifactorial causation
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7. Indirect association
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8. Example of confounder
• Higher maternal age is directly associated with
Down's Syndrome in the child
• Higher maternal age is directly associated with
Down's Syndrome, regardless of birth order
• Maternal age is directly associated with birth order
• Maternal age is not a consequence of birth order
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9. Cause
• A cause is something which has an effect
• In epidemiology a cause can be considered to
be something that alters the frequency of
disease, health status or associated factors in
a population
• Necessary and sufficient to produce effect
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10. Multifactorial causation
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Factor 1
Factor 2
Factor 3
Critical change at
cellular level
Disease

11. Multifactorial causation
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Factor 1 Factor 3
Critical change at
cellular level
Disease
Factor 2

12. Hills criteria
1. Temporality
2. Strength
3. Specificity
4. Consistency
5. Biological plausibility
6. Coherence
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13. 1. Temporality
• Cause always precedes effect
• Easy to establish in acute disease, difficult in
chronic disease
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14. 2. Strength
• Relative risk
• Dose-response
• Duration response
• Cessation experiment
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15. 3. Specificity
• Not relevant these days
• Due to multifactorial causation theories
• ‘not everyone who smokes develops lung
cancer and not everyone who develops cancer
smokes.’
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16. 4. Consistency
• Different methods
• Different locations
• Different disciplines
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17. 5. Biological plausibility
• The mechanism which relates cause to effect
with the help of existing knowledge
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18. 6. Coherence
• With already known facts from multiple
sources
• Evidences from elsewhere
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19. Uses of epidemiology
1. To study historically the rise and fall of
disease
2. Community diagnosis
3. Planning and evaluation
4. Evaluation of individual's risks and chances
5. Syndrome identification
6. Completing the natural history of disease
7. Searching for causes and risk factors
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20. THANKS FOR LISTENING
Email your doubts to: sarizwan1986@outlook.com
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