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Association & Causation
‘omne ignotum pro magnifico’
Dr. Rizwan S A, M.D.,
Assistant Professor,
Department of Community Medicine,
VMCH&RI, Madurai.
03.11.2014
II MBBS Epidemiology series 1
Classification of research methods
Research
methods
Observational
Descriptive
Case series,
case reports,
CS, cohort
Analytical
Ecological Cross-
sectional
Cohort Case control
Experimental
Controlled Uncontrolled
II MBBS, Epidemiology series 2
Procedures in descriptive epidemiology
1. Define the population
2. Define and describe the disease
3. Measure the disease
4. Compare
5. Formulate hypothesis
II MBBS, Epidemiology series 3
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
II MBBS Epidemiology series 4
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
II MBBS Epidemiology series 5
Types of association
1. Spurious association
2. Indirect association
3. Direct (causal) association
I. One to one causal association
II. Multifactorial causation
II MBBS Epidemiology series 6
Indirect association
II MBBS Epidemiology series 7
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
II MBBS Epidemiology series 8
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
II MBBS Epidemiology series 9
Multifactorial causation
II MBBS Epidemiology series 10
Factor 1
Factor 2
Factor 3
Critical change at
cellular level
Disease
Multifactorial causation
II MBBS Epidemiology series 11
Factor 1 Factor 3
Critical change at
cellular level
Disease
Factor 2
Hills criteria
1. Temporality
2. Strength
3. Specificity
4. Consistency
5. Biological plausibility
6. Coherence
II MBBS Epidemiology series 12
1. Temporality
• Cause always precedes effect
• Easy to establish in acute disease, difficult in
chronic disease
II MBBS Epidemiology series 13
2. Strength
• Relative risk
• Dose-response
• Duration response
• Cessation experiment
II MBBS Epidemiology series 14
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.’
II MBBS Epidemiology series 15
4. Consistency
• Different methods
• Different locations
• Different disciplines
II MBBS Epidemiology series 16
5. Biological plausibility
• The mechanism which relates cause to effect
with the help of existing knowledge
II MBBS Epidemiology series 17
6. Coherence
• With already known facts from multiple
sources
• Evidences from elsewhere
II MBBS Epidemiology series 18
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
II MBBS Epidemiology series 19
THANKS FOR LISTENING
Email your doubts to: sarizwan1986@outlook.com
II MBBS, Epidemiology series 20

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Association and Causation

  • 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 II MBBS Epidemiology series 1
  • 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 II MBBS, Epidemiology series 2
  • 3. Procedures in descriptive epidemiology 1. Define the population 2. Define and describe the disease 3. Measure the disease 4. Compare 5. Formulate hypothesis II MBBS, Epidemiology series 3
  • 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 II MBBS Epidemiology series 4
  • 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 II MBBS Epidemiology series 5
  • 6. Types of association 1. Spurious association 2. Indirect association 3. Direct (causal) association I. One to one causal association II. Multifactorial causation II MBBS Epidemiology series 6
  • 7. Indirect association II MBBS Epidemiology series 7
  • 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 II MBBS Epidemiology series 8
  • 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 II MBBS Epidemiology series 9
  • 10. Multifactorial causation II MBBS Epidemiology series 10 Factor 1 Factor 2 Factor 3 Critical change at cellular level Disease
  • 11. Multifactorial causation II MBBS Epidemiology series 11 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 II MBBS Epidemiology series 12
  • 13. 1. Temporality • Cause always precedes effect • Easy to establish in acute disease, difficult in chronic disease II MBBS Epidemiology series 13
  • 14. 2. Strength • Relative risk • Dose-response • Duration response • Cessation experiment II MBBS Epidemiology series 14
  • 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.’ II MBBS Epidemiology series 15
  • 16. 4. Consistency • Different methods • Different locations • Different disciplines II MBBS Epidemiology series 16
  • 17. 5. Biological plausibility • The mechanism which relates cause to effect with the help of existing knowledge II MBBS Epidemiology series 17
  • 18. 6. Coherence • With already known facts from multiple sources • Evidences from elsewhere II MBBS Epidemiology series 18
  • 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 II MBBS Epidemiology series 19
  • 20. THANKS FOR LISTENING Email your doubts to: sarizwan1986@outlook.com II MBBS, Epidemiology series 20