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Association and causation


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Association and causation

  2. 2. INTRODUCTION Association is the concurrence of two variables more often than would be expected by chance. Events are said to be associated when they occur more frequently together than one would expect by chance 2
  3. 3. TYPES Spurious Indirect Direct  One-to-one  multifactorial 3
  4. 4. SPURIOUS ASSOCIATION Appears due to improper comparison Observed association between a disease & suspected factor may not be real. 4
  5. 5. INDIRECT ASSOCIATION Statistical association between a character of interest and a disease due to presence of another factor, known or unknown, that is common to both the factors. Altitude Iodine deficiency Endemic goitre 5
  6. 6. DIRECT ASSOCIATION Between two attributes that are directly related to each other. One-to-one causation: when disease is present, factor must also be present. e.g., Hemolytic streptococci causing tonsillitis, scarlet fever, erysipelas Multifactorial causation: alternative causative factors acting independently. e.g., lung cancer being caused by smoking, air pollutants. 6
  7. 7. CRITERIA FOR JUDGING CAUSALITYBradford Hill report, 1964  Temporal association  Strength of association  Specificity of association  Consistency of association  Biological plausability  Coherence of association 7
  8. 8. TEMPORAL ASSOCIATION Causal attribute must precede the disease or unfavourable outcome Exposure to factor must have occurred before the disease developed 8
  9. 9. STRENGTH OF ASSOCIATION If the association is strong or weak With increased level of exposure to risk factor, incidence of disease increases. 9
  10. 10. SPECIFICITY OF ASSOCIATION One to one relation between cause and effect Weakest of the criteria 10
  11. 11. CONSISTENCY OF ASSOCIATION Occurrence of association at some other time & place repeatedly. If a relationship is causal, findings should be consistent with other data. 11
  12. 12. BIOLOGICAL PLAUSABILITY Association must be consistent with other knowledge like mechanism of action, evidence from animal experiments etc. 12
  13. 13. COHERENCE OF ASSOCIATION Causal significance of an association is its unity with known facts that are thought to be related. 13
  14. 14. THANK YOU THANK YOU for reading my presentation. If you have any doubts or interesting cases in any subject of medicine, I will be delighted if you share at 14