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Association and Causation

II MBBS class - epidemiology series

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Association and Causation

  1. 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. 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. 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. 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. 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. 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. 7. Indirect association II MBBS Epidemiology series 7
  8. 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. 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. 10. Multifactorial causation II MBBS Epidemiology series 10 Factor 1 Factor 2 Factor 3 Critical change at cellular level Disease
  11. 11. Multifactorial causation II MBBS Epidemiology series 11 Factor 1 Factor 3 Critical change at cellular level Disease Factor 2
  12. 12. Hills criteria 1. Temporality 2. Strength 3. Specificity 4. Consistency 5. Biological plausibility 6. Coherence II MBBS Epidemiology series 12
  13. 13. 1. Temporality • Cause always precedes effect • Easy to establish in acute disease, difficult in chronic disease II MBBS Epidemiology series 13
  14. 14. 2. Strength • Relative risk • Dose-response • Duration response • Cessation experiment II MBBS Epidemiology series 14
  15. 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. 16. 4. Consistency • Different methods • Different locations • Different disciplines II MBBS Epidemiology series 16
  17. 17. 5. Biological plausibility • The mechanism which relates cause to effect with the help of existing knowledge II MBBS Epidemiology series 17
  18. 18. 6. Coherence • With already known facts from multiple sources • Evidences from elsewhere II MBBS Epidemiology series 18
  19. 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. 20. THANKS FOR LISTENING Email your doubts to: sarizwan1986@outlook.com II MBBS, Epidemiology series 20

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